diff --git a/.github/workflows/continuous-synth-e2e.yml b/.github/workflows/continuous-synth-e2e.yml
new file mode 100644
index 00000000..e477214a
--- /dev/null
+++ b/.github/workflows/continuous-synth-e2e.yml
@@ -0,0 +1,160 @@
+name: Continuous synthetic E2E (staging)
+
+# Hard gate (#2342): cron-driven full-lifecycle E2E that catches
+# regressions visible only at runtime — schema drift, deployment-pipeline
+# gaps, vendor outages, env-var rotations, DNS / CF / Railway side-effects.
+#
+# Why this gate exists:
+#   PR-time CI catches code-level regressions but not deployment-time or
+#   integration-time ones. Today's empirical data:
+#     • #2345 (A2A v0.2 silent drop) — passed all unit tests, broke at
+#       JSON-RPC parse layer between sender and receiver. Visible only
+#       to a sender exercising the full path.
+#     • RFC #2312 chat upload — landed on staging-branch but never
+#       reached staging tenants because publish-workspace-server-image
+#       was main-only. Caught by manual dogfooding hours after deploy.
+#   Both would have surfaced within 15-20 min of regression if a
+#   continuous synth-E2E was running.
+#
+# Cadence: every 20 min (3x/hour). The script is conservatively
+# bounded at 10 min wall-clock; even on degraded staging it should
+# finish before the next firing. cron-overlap is guarded by the
+# concurrency group below.
+#
+# Cost: ~3 runs/hour × 5-10 min × $0.008/min GHA = ~$0.50-$1/day.
+# Plus a fresh tenant provisioned + torn down each run (Railway +
+# AWS pennies). Negligible.
+#
+# Failure handling: when the run fails, the workflow exits non-zero
+# and GitHub's standard email/notification path fires. Operators
+# can subscribe to this workflow's failure channel for paging-grade
+# alerting.
+
+on:
+  schedule:
+    # Every 20 minutes, on the :00 :20 :40. Offsets the existing :15
+    # sweep-cf-orphans and :45 sweep-cf-tunnels so the three
+    # operations don't all hit Cloudflare/AWS at the same minute.
+    - cron: '0,20,40 * * * *'
+  workflow_dispatch:
+    inputs:
+      runtime:
+        description: "Runtime to provision (langgraph = fastest, default; hermes = slower but covers SDK-native path; claude-code = needs OAUTH token in tenant env)"
+        required: false
+        default: "langgraph"
+        type: string
+      keep_org:
+        description: "Skip teardown for post-mortem debugging (only manual dispatch — never set this for cron runs)"
+        required: false
+        default: false
+        type: boolean
+
+permissions:
+  contents: read
+  # No issue-write here — failures surface as red runs in the workflow
+  # history. If you want auto-issue-on-fail, add a follow-up step that
+  # uses gh issue create gated on `if: failure()`. Keeping the surface
+  # minimal until that's actually wanted.
+
+# Serialize so two firings can never overlap. Cron firing every 20 min
+# but scripts conservatively bounded at 10 min — overlap shouldn't
+# happen in steady state, but if a run hangs we don't want N more
+# stacking up.
+concurrency:
+  group: continuous-synth-e2e
+  cancel-in-progress: false
+
+jobs:
+  synth:
+    name: Synthetic E2E against staging
+    runs-on: ubuntu-latest
+    timeout-minutes: 12
+    env:
+      # langgraph default keeps cold-start under 5 min on staging EC2.
+      # hermes is slower (~7-10 min) and isn't needed for the
+      # regression class this gate exists to catch (deployment-pipeline
+      # + schema-drift + integration). Operators can pick hermes via
+      # workflow_dispatch when they need to exercise the SDK-native
+      # session path.
+      E2E_RUNTIME: ${{ github.event.inputs.runtime || 'langgraph' }}
+      # Bound to 10 min so a stuck provision fails the run instead of
+      # holding up the next cron firing. 15-min default in the script
+      # is for the on-PR full lifecycle where we have more headroom.
+      E2E_PROVISION_TIMEOUT_SECS: '600'
+      # Slug suffix — namespaced "synth-" so these runs are
+      # distinguishable from PR-driven runs in CP admin.
+      E2E_RUN_ID: synth-${{ github.run_id }}
+      # Forced false for cron; respected for manual dispatch
+      E2E_KEEP_ORG: ${{ github.event.inputs.keep_org == 'true' && '1' || '' }}
+      MOLECULE_CP_URL: ${{ vars.STAGING_CP_URL || 'https://staging-api.moleculesai.app' }}
+      MOLECULE_ADMIN_TOKEN: ${{ secrets.CP_STAGING_ADMIN_API_TOKEN }}
+    steps:
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+
+      - name: Verify required secret present
+        run: |
+          # Schedule-vs-dispatch hardening (mirrors the sweep-cf-* and
+          # redeploy-tenants-on-* workflows): hard-fail on missing secret
+          # for cron firing so a misconfigured-repo doesn't silently
+          # report green while doing nothing. Soft-skip on operator
+          # dispatch — operators can dispatch ad-hoc to verify a fix
+          # without setting up the secret first.
+          if [ -z "${MOLECULE_ADMIN_TOKEN:-}" ]; then
+            if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
+              echo "::warning::CP_STAGING_ADMIN_API_TOKEN not set — synth E2E cannot run"
+              echo "::warning::Set it at Settings → Secrets and Variables → Actions"
+              exit 0
+            fi
+            echo "::error::CP_STAGING_ADMIN_API_TOKEN secret missing — synth E2E cannot run"
+            echo "::error::Set it at Settings → Secrets and Variables → Actions; pull from staging-CP's CP_ADMIN_API_TOKEN env in Railway."
+            exit 1
+          fi
+
+      - name: Install required tools
+        run: |
+          # The script depends on jq + curl (already on ubuntu-latest)
+          # and python3 (likewise). Verify they're all present so we
+          # fail fast on a runner image regression rather than mid-script.
+          for cmd in jq curl python3; do
+            command -v "$cmd" >/dev/null 2>&1 || {
+              echo "::error::required tool '$cmd' not on PATH — runner image regression?"
+              exit 1
+            }
+          done
+
+      - name: Run synthetic E2E
+        # The script handles its own teardown via EXIT trap; even on
+        # failure (timeout, assertion), the org is deprovisioned and
+        # leaks are reported. Exit code propagates from the script.
+        run: |
+          bash tests/e2e/test_staging_full_saas.sh
+
+      - name: Failure summary
+        # Runs only on failure. Adds a job summary so the workflow run
+        # page shows a quick "what happened" instead of forcing readers
+        # to scroll through script output.
+        if: failure()
+        run: |
+          {
+            echo "## Continuous synth E2E failed"
+            echo ""
+            echo "**Run ID:** ${{ github.run_id }}"
+            echo "**Trigger:** ${{ github.event_name }}"
+            echo "**Runtime:** ${E2E_RUNTIME}"
+            echo "**Slug:** synth-${{ github.run_id }}"
+            echo ""
+            echo "### What this means"
+            echo ""
+            echo "Staging just regressed on a path that previously worked. Likely classes:"
+            echo "- Schema mismatch between sender and receiver (#2345 class)"
+            echo "- Deployment-pipeline gap (RFC #2312 / staging-tenant-image-stale class)"
+            echo "- Vendor outage (Cloudflare, Railway, AWS, GHCR)"
+            echo "- Staging-CP env var rotation"
+            echo ""
+            echo "### Next steps"
+            echo ""
+            echo "1. Check the script output above for the assertion that failed"
+            echo "2. If it's a vendor outage, no action needed — next firing in ~20 min"
+            echo "3. If it's a code regression, find the causing PR via \`git log\` against last green run and revert/fix"
+            echo "4. Keep an eye on the next 1-2 firings — flake vs persistent fail differs in priority"
+          } >> "$GITHUB_STEP_SUMMARY"
diff --git a/workspace-server/internal/db/architecture_test.go b/workspace-server/internal/db/architecture_test.go
new file mode 100644
index 00000000..d585db62
--- /dev/null
+++ b/workspace-server/internal/db/architecture_test.go
@@ -0,0 +1,63 @@
+package db_test
+
+// Architecture test (#2344): db is a leaf — DB pool + migrations + raw
+// SQL helpers, no business-logic dependencies. The DB layer must be
+// testable with sqlmock in isolation. If db starts importing handlers
+// or provisioner, every db unit test would need to bring up that
+// subsystem, and the layering becomes circular.
+//
+// If this test fails: you put business logic in the db package. Move
+// it to a higher-tier package that imports db, not the reverse.
+
+import (
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const moduleInternalPrefix = "github.com/Molecule-AI/molecule-monorepo/platform/internal/"
+
+func TestDBHasNoInternalDependencies(t *testing.T) {
+	t.Parallel()
+	for path, file := range listImports(t, ".") {
+		if strings.HasPrefix(path, moduleInternalPrefix) {
+			t.Errorf(
+				"db must not import other internal packages "+
+					"(found %q in %s) — db is the foundation layer and a "+
+					"reverse dep creates a cycle (everything imports db). "+
+					"See workspace-server/internal/db/architecture_test.go.",
+				path, file,
+			)
+		}
+	}
+}
+
+func listImports(t *testing.T, dir string) map[string]string {
+	t.Helper()
+	fset := token.NewFileSet()
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		t.Fatalf("read %s: %v", dir, err)
+	}
+	out := make(map[string]string)
+	for _, e := range entries {
+		name := e.Name()
+		if e.IsDir() || !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {
+			continue
+		}
+		f, err := parser.ParseFile(fset, filepath.Join(dir, name), nil, parser.ImportsOnly)
+		if err != nil {
+			t.Fatalf("parse %s: %v", name, err)
+		}
+		for _, imp := range f.Imports {
+			path := strings.Trim(imp.Path.Value, "\"")
+			if _, seen := out[path]; !seen {
+				out[path] = name
+			}
+		}
+	}
+	return out
+}
diff --git a/workspace-server/internal/handlers/a2a_proxy.go b/workspace-server/internal/handlers/a2a_proxy.go
index 4a7c8026..3389cb96 100644
--- a/workspace-server/internal/handlers/a2a_proxy.go
+++ b/workspace-server/internal/handlers/a2a_proxy.go
@@ -21,6 +21,7 @@ import (
 
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/db"
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/events"
+	"github.com/Molecule-AI/molecule-monorepo/platform/internal/models"
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/provisioner"
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/registry"
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/wsauth"
@@ -305,17 +306,54 @@ func (h *WorkspaceHandler) proxyA2ARequest(ctx context.Context, workspaceID stri
 		return 0, nil, proxyErr
 	}
 
-	agentURL, proxyErr := h.resolveAgentURL(ctx, workspaceID)
-	if proxyErr != nil {
-		return 0, nil, proxyErr
-	}
-
+	// Normalize the JSON-RPC envelope BEFORE the poll-mode short-circuit
+	// so the activity_logs entry carries the protocol method name (initialize,
+	// message/send, etc.) — the polling agent uses that to dispatch the
+	// request body to the right handler. Doing it here also means a
+	// malformed payload fails the same way for push and poll callers
+	// (consistent 400 instead of "queued garbage").
 	normalizedBody, a2aMethod, proxyErr := normalizeA2APayload(body)
 	if proxyErr != nil {
 		return 0, nil, proxyErr
 	}
 	body = normalizedBody
 
+	// #2339 PR 2 — poll-mode short-circuit. When the target workspace
+	// is registered as delivery_mode=poll (e.g. an operator's laptop
+	// running molecule-mcp-claude-channel), the platform does NOT
+	// dispatch over HTTP — the agent has no public URL. Instead we record
+	// the A2A request to activity_logs and the agent picks it up via
+	// GET /activity?since_id= (PR 3).
+	//
+	// Returning here means we skip resolveAgentURL entirely (no SSRF check
+	// needed — there's no URL to validate; no DNS lookup against potentially-
+	// changing operator-side IPs) and skip the dispatch path completely
+	// (no Do(), no maybeMarkContainerDead). The response is a synthetic
+	// {status:"queued"} envelope so the caller (canvas, another workspace)
+	// knows delivery is acknowledged but pending consumption.
+	if lookupDeliveryMode(ctx, workspaceID) == models.DeliveryModePoll {
+		if logActivity {
+			h.logA2AReceiveQueued(ctx, workspaceID, callerID, body, a2aMethod)
+		}
+		respBody, marshalErr := json.Marshal(gin.H{
+			"status":        "queued",
+			"delivery_mode": models.DeliveryModePoll,
+			"method":        a2aMethod,
+		})
+		if marshalErr != nil {
+			return 0, nil, &proxyA2AError{
+				Status:   http.StatusInternalServerError,
+				Response: gin.H{"error": "failed to marshal poll-mode response"},
+			}
+		}
+		return http.StatusOK, respBody, nil
+	}
+
+	agentURL, proxyErr := h.resolveAgentURL(ctx, workspaceID)
+	if proxyErr != nil {
+		return 0, nil, proxyErr
+	}
+
 	startTime := time.Now()
 	resp, cancelFwd, err := h.dispatchA2A(ctx, workspaceID, agentURL, body, callerID)
 	if cancelFwd != nil {
@@ -486,11 +524,54 @@ func normalizeA2APayload(body []byte) ([]byte, string, *proxyA2AError) {
 	}
 
 	// Ensure params.message.messageId exists (required by a2a-sdk)
+	// AND v0.2→v0.3 compat (#2345): when sender supplies
+	// params.message.content (v0.2) instead of params.message.parts
+	// (v0.3), wrap the content as a single text Part so the downstream
+	// a2a-sdk's v0.3 Pydantic validator accepts the message.
+	//
+	// Pre-fix: Design Director silently dropped briefs whose sender
+	// used v0.2 shape — Pydantic rejected at parse time, the rejection
+	// went only to logs, and the sender saw a happy 200/202.
+	//
+	// Reject loud (HTTP 400) when neither content nor parts is present;
+	// previously the SDK's own rejection happened post-handler-dispatch
+	// and was invisible to the original sender.
 	if params, ok := payload["params"].(map[string]interface{}); ok {
 		if msg, ok := params["message"].(map[string]interface{}); ok {
 			if _, hasID := msg["messageId"]; !hasID {
 				msg["messageId"] = uuid.New().String()
 			}
+			_, hasParts := msg["parts"]
+			rawContent, hasContent := msg["content"]
+			if !hasParts {
+				if hasContent {
+					switch v := rawContent.(type) {
+					case string:
+						msg["parts"] = []interface{}{
+							map[string]interface{}{"kind": "text", "text": v},
+						}
+					case []interface{}:
+						msg["parts"] = v
+					default:
+						return nil, "", &proxyA2AError{
+							Status: http.StatusBadRequest,
+							Response: gin.H{
+								"error": "invalid params.message.content type",
+								"hint":  "content must be a string (v0.2 compat) or omitted in favour of parts (v0.3)",
+							},
+						}
+					}
+					delete(msg, "content")
+				} else {
+					return nil, "", &proxyA2AError{
+						Status: http.StatusBadRequest,
+						Response: gin.H{
+							"error": "params.message must contain either 'parts' (v0.3) or 'content' (v0.2 compat)",
+							"hint":  "v0.3 example: {\"parts\":[{\"kind\":\"text\",\"text\":\"...\"}]}",
+						},
+					}
+				}
+			}
 		}
 	}
 
diff --git a/workspace-server/internal/handlers/a2a_proxy_helpers.go b/workspace-server/internal/handlers/a2a_proxy_helpers.go
index 3e67667f..d0ccea86 100644
--- a/workspace-server/internal/handlers/a2a_proxy_helpers.go
+++ b/workspace-server/internal/handlers/a2a_proxy_helpers.go
@@ -5,6 +5,7 @@ package handlers
 
 import (
 	"context"
+	"database/sql"
 	"encoding/json"
 	"errors"
 	"log"
@@ -13,6 +14,7 @@ import (
 	"time"
 
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/db"
+	"github.com/Molecule-AI/molecule-monorepo/platform/internal/models"
 	"github.com/Molecule-AI/molecule-monorepo/platform/internal/wsauth"
 	"github.com/gin-gonic/gin"
 )
@@ -376,6 +378,74 @@ func parseUsageFromA2AResponse(body []byte) (inputTokens, outputTokens int64) {
 	return 0, 0
 }
 
+// lookupDeliveryMode returns the workspace's delivery_mode. On any DB
+// error or missing row it returns DeliveryModePush — the fail-closed
+// default. "Closed" here means "fall back to today's behavior (synchronous
+// dispatch)" rather than "fall back to drop the request silently into
+// activity_logs where the agent might never see it." A poll-mode workspace
+// that briefly reads as push will get its A2A request dispatched to the
+// stored URL (or a 502 if no URL); a push-mode workspace that briefly
+// reads as poll would get its request silently queued with no dispatch.
+// The first failure is loud + recoverable; the second is silent.
+//
+// The function is intentionally lookup-only — it never mutates the row.
+// The register handler (registry.go) is the only writer for delivery_mode.
+//
+// See #2339 PR 1 for the column + register-flow side; this is the
+// proxy-side read used for the short-circuit in proxyA2ARequest.
+func lookupDeliveryMode(ctx context.Context, workspaceID string) string {
+	var mode sql.NullString
+	err := db.DB.QueryRowContext(ctx,
+		`SELECT delivery_mode FROM workspaces WHERE id = $1`, workspaceID,
+	).Scan(&mode)
+	if err != nil {
+		if !errors.Is(err, sql.ErrNoRows) {
+			log.Printf("ProxyA2A: lookupDeliveryMode(%s) failed (%v) — defaulting to push", workspaceID, err)
+		}
+		return models.DeliveryModePush
+	}
+	if !mode.Valid || mode.String == "" {
+		return models.DeliveryModePush
+	}
+	if !models.IsValidDeliveryMode(mode.String) {
+		log.Printf("ProxyA2A: workspace %s has invalid delivery_mode=%q — defaulting to push", workspaceID, mode.String)
+		return models.DeliveryModePush
+	}
+	return mode.String
+}
+
+// logA2AReceiveQueued records a poll-mode "queued" A2A receive into
+// activity_logs. Same shape as logA2ASuccess but without ResponseBody
+// (there is no response yet — the polling agent will produce one when
+// it picks the request up). status="ok" because the request was
+// successfully queued; the consume side reports its own outcome.
+//
+// The activity_logs row is what the polling agent's GET /activity?since_id=
+// reads in PR 3 — that's how a poll-mode workspace receives inbound A2A
+// without a public URL.
+func (h *WorkspaceHandler) logA2AReceiveQueued(ctx context.Context, workspaceID, callerID string, body []byte, a2aMethod string) {
+	var wsName string
+	db.DB.QueryRowContext(ctx, `SELECT name FROM workspaces WHERE id = $1`, workspaceID).Scan(&wsName)
+	if wsName == "" {
+		wsName = workspaceID
+	}
+	summary := a2aMethod + " → " + wsName + " (queued for poll)"
+	go func(parent context.Context) {
+		logCtx, cancel := context.WithTimeout(context.WithoutCancel(parent), 30*time.Second)
+		defer cancel()
+		LogActivity(logCtx, h.broadcaster, ActivityParams{
+			WorkspaceID:  workspaceID,
+			ActivityType: "a2a_receive",
+			SourceID:     nilIfEmpty(callerID),
+			TargetID:     &workspaceID,
+			Method:       &a2aMethod,
+			Summary:      &summary,
+			RequestBody:  json.RawMessage(body),
+			Status:       "ok",
+		})
+	}(ctx)
+}
+
 // readUsageMap extracts input_tokens / output_tokens from the "usage" key of m.
 // Returns (0, 0, false) when the key is absent or contains no non-zero values.
 func readUsageMap(m map[string]json.RawMessage) (inputTokens, outputTokens int64, ok bool) {
diff --git a/workspace-server/internal/handlers/a2a_proxy_test.go b/workspace-server/internal/handlers/a2a_proxy_test.go
index 1a33a866..9d0b6e28 100644
--- a/workspace-server/internal/handlers/a2a_proxy_test.go
+++ b/workspace-server/internal/handlers/a2a_proxy_test.go
@@ -11,6 +11,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"os"
+	"strings"
 	"testing"
 	"time"
 
@@ -1137,7 +1138,10 @@ func TestNormalizeA2APayload_PreservesExistingMessageId(t *testing.T) {
 }
 
 func TestNormalizeA2APayload_MissingMethodReturnsEmpty(t *testing.T) {
-	raw := []byte(`{"params":{"message":{"role":"user"}}}`)
+	// Method extraction returns empty string when method is absent,
+	// regardless of message validity. Include parts: [] so the v0.2→v0.3
+	// compat check (#2345) doesn't reject before method extraction.
+	raw := []byte(`{"params":{"message":{"role":"user","parts":[]}}}`)
 	_, method, perr := normalizeA2APayload(raw)
 	if perr != nil {
 		t.Fatalf("unexpected error: %+v", perr)
@@ -1147,6 +1151,102 @@ func TestNormalizeA2APayload_MissingMethodReturnsEmpty(t *testing.T) {
 	}
 }
 
+// --- v0.2 → v0.3 compat shim (#2345) ---
+
+func TestNormalizeA2APayload_ConvertsV02StringContentToParts(t *testing.T) {
+	raw := []byte(`{"method":"message/send","params":{"message":{"role":"user","content":"hello world"}}}`)
+	out, _, perr := normalizeA2APayload(raw)
+	if perr != nil {
+		t.Fatalf("unexpected error: %+v", perr)
+	}
+	var parsed map[string]interface{}
+	if err := json.Unmarshal(out, &parsed); err != nil {
+		t.Fatalf("output not valid JSON: %v", err)
+	}
+	msg := parsed["params"].(map[string]interface{})["message"].(map[string]interface{})
+	if _, stillHasContent := msg["content"]; stillHasContent {
+		t.Error("v0.2 'content' field should be removed after conversion")
+	}
+	parts, ok := msg["parts"].([]interface{})
+	if !ok || len(parts) != 1 {
+		t.Fatalf("expected 1 part, got %v", msg["parts"])
+	}
+	part := parts[0].(map[string]interface{})
+	if part["kind"] != "text" || part["text"] != "hello world" {
+		t.Errorf("expected {kind:text, text:'hello world'}, got %v", part)
+	}
+}
+
+func TestNormalizeA2APayload_ConvertsV02ListContentToParts(t *testing.T) {
+	raw := []byte(`{"method":"message/send","params":{"message":{"role":"user","content":[{"kind":"text","text":"hi"}]}}}`)
+	out, _, perr := normalizeA2APayload(raw)
+	if perr != nil {
+		t.Fatalf("unexpected error: %+v", perr)
+	}
+	var parsed map[string]interface{}
+	_ = json.Unmarshal(out, &parsed)
+	msg := parsed["params"].(map[string]interface{})["message"].(map[string]interface{})
+	parts, ok := msg["parts"].([]interface{})
+	if !ok || len(parts) != 1 {
+		t.Fatalf("expected list preserved as parts, got %v", msg["parts"])
+	}
+}
+
+func TestNormalizeA2APayload_PreservesV03Parts(t *testing.T) {
+	raw := []byte(`{"method":"message/send","params":{"message":{"role":"user","parts":[{"kind":"text","text":"hi"}]}}}`)
+	out, _, perr := normalizeA2APayload(raw)
+	if perr != nil {
+		t.Fatalf("unexpected error: %+v", perr)
+	}
+	var parsed map[string]interface{}
+	_ = json.Unmarshal(out, &parsed)
+	msg := parsed["params"].(map[string]interface{})["message"].(map[string]interface{})
+	if _, hasContent := msg["content"]; hasContent {
+		t.Error("did not expect content field in v0.3-shaped payload output")
+	}
+	parts := msg["parts"].([]interface{})
+	if len(parts) != 1 {
+		t.Errorf("expected 1 part preserved, got %d", len(parts))
+	}
+}
+
+func TestNormalizeA2APayload_RejectsMessageWithNeitherContentNorParts(t *testing.T) {
+	raw := []byte(`{"method":"message/send","params":{"message":{"role":"user","metadata":{}}}}`)
+	_, _, perr := normalizeA2APayload(raw)
+	if perr == nil {
+		t.Fatal("expected error for message with neither content nor parts")
+	}
+	if perr.Status != http.StatusBadRequest {
+		t.Errorf("expected 400, got %d", perr.Status)
+	}
+	errMsg, _ := perr.Response["error"].(string)
+	if !strings.Contains(errMsg, "parts") || !strings.Contains(errMsg, "content") {
+		t.Errorf("error message should mention both 'parts' and 'content', got: %q", errMsg)
+	}
+}
+
+func TestNormalizeA2APayload_RejectsContentWithUnsupportedType(t *testing.T) {
+	raw := []byte(`{"method":"message/send","params":{"message":{"role":"user","content":42}}}`)
+	_, _, perr := normalizeA2APayload(raw)
+	if perr == nil {
+		t.Fatal("expected error for non-string non-list content")
+	}
+	if perr.Status != http.StatusBadRequest {
+		t.Errorf("expected 400, got %d", perr.Status)
+	}
+}
+
+func TestNormalizeA2APayload_NoMessageNoCheck(t *testing.T) {
+	raw := []byte(`{"method":"tasks/list","params":{}}`)
+	_, method, perr := normalizeA2APayload(raw)
+	if perr != nil {
+		t.Fatalf("unexpected error on params-message-absent payload: %+v", perr)
+	}
+	if method != "tasks/list" {
+		t.Errorf("expected method=tasks/list, got %q", method)
+	}
+}
+
 // --- resolveAgentURL direct unit tests ---
 
 func TestResolveAgentURL_CacheHit(t *testing.T) {
@@ -1704,3 +1804,185 @@ func TestResolveAgentURL_HibernatedWorkspace_NullURLVariant(t *testing.T) {
 		t.Errorf("unmet DB expectations: %v", err)
 	}
 }
+
+// ==================== ProxyA2A — poll-mode short-circuit (#2339 PR 2) ====================
+
+// TestProxyA2A_PollMode_ShortCircuits_NoSSRF_NoDispatch verifies the core
+// invariant of #2339 PR 2: when delivery_mode=poll, ProxyA2A must NOT
+// hit resolveAgentURL (which would SSRF-check or 502 on a missing URL)
+// and must NOT dispatch over HTTP. It records the request to activity_logs
+// and returns 200 {status:"queued"} instead.
+//
+// Without this short-circuit, the canvas chat fails for any workspace
+// running molecule-mcp-claude-channel (operator's laptop, no public URL):
+// resolveAgentURL would 502 on the missing URL and the polling agent
+// would never see the inbound message. That's the bug PR 2 fixes.
+func TestProxyA2A_PollMode_ShortCircuits_NoSSRF_NoDispatch(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
+
+	const wsID = "ws-poll-shortcircuit"
+
+	// Budget check still runs (above the short-circuit) — affirms the
+	// budget guard is mode-agnostic, which is correct: a poll-mode
+	// workspace shouldn't burn unmetered platform CPU/storage either.
+	expectBudgetCheck(mock, wsID)
+
+	// lookupDeliveryMode SELECT — returns poll, triggering the short-circuit.
+	// Note: NO ExpectQuery for `SELECT url, status FROM workspaces` (that's
+	// resolveAgentURL's query) — the short-circuit must skip resolveAgentURL.
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"delivery_mode"}).AddRow("poll"))
+
+	// Activity log: the queued receive (logA2AReceiveQueued in helpers.go).
+	mock.ExpectExec("INSERT INTO activity_logs").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: wsID}}
+
+	body := `{"jsonrpc":"2.0","id":"poll-1","method":"message/send","params":{"message":{"role":"user","parts":[{"text":"hi"}]}}}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/"+wsID+"/a2a", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.ProxyA2A(c)
+
+	time.Sleep(50 * time.Millisecond)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200 (queued), got %d: %s", w.Code, w.Body.String())
+	}
+
+	var resp map[string]interface{}
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("response is not valid JSON: %v", err)
+	}
+	if resp["status"] != "queued" {
+		t.Errorf("response.status = %v, want %q", resp["status"], "queued")
+	}
+	if resp["delivery_mode"] != "poll" {
+		t.Errorf("response.delivery_mode = %v, want %q", resp["delivery_mode"], "poll")
+	}
+	if resp["method"] != "message/send" {
+		t.Errorf("response.method = %v, want %q (the JSON-RPC method that was queued)", resp["method"], "message/send")
+	}
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet sqlmock expectations: %v", err)
+	}
+}
+
+// TestProxyA2A_PushMode_NoShortCircuit verifies the symmetric contract:
+// a push-mode workspace (default) is NOT affected by the new short-circuit.
+// It still proceeds to resolveAgentURL + dispatch. Without this guard, a
+// regression in lookupDeliveryMode could silently break the entire fleet.
+func TestProxyA2A_PushMode_NoShortCircuit(t *testing.T) {
+	mock := setupTestDB(t)
+	mr := setupTestRedis(t)
+	allowLoopbackForTest(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
+
+	const wsID = "ws-push-default"
+
+	dispatched := false
+	agentServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		dispatched = true
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprint(w, `{"jsonrpc":"2.0","id":"1","result":{"status":"ok"}}`)
+	}))
+	defer agentServer.Close()
+
+	mr.Set(fmt.Sprintf("ws:%s:url", wsID), agentServer.URL)
+	expectBudgetCheck(mock, wsID)
+
+	// lookupDeliveryMode returns "push" — short-circuit must NOT fire.
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"delivery_mode"}).AddRow("push"))
+
+	mock.ExpectExec("INSERT INTO activity_logs").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: wsID}}
+
+	body := `{"jsonrpc":"2.0","id":"push-1","method":"message/send","params":{"message":{"role":"user","parts":[{"text":"hi"}]}}}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/"+wsID+"/a2a", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.ProxyA2A(c)
+
+	time.Sleep(50 * time.Millisecond)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200 (dispatched), got %d: %s", w.Code, w.Body.String())
+	}
+	if !dispatched {
+		t.Error("push-mode workspace: expected the agent server to receive the request, but it did not")
+	}
+	var resp map[string]interface{}
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err == nil {
+		if resp["status"] == "queued" {
+			t.Error("push-mode response leaked queued envelope — short-circuit fired when it shouldn't have")
+		}
+	}
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet sqlmock expectations: %v", err)
+	}
+}
+
+// TestProxyA2A_PollMode_FailsClosedToPush verifies the safety contract:
+// a DB error reading delivery_mode must default to push (the existing
+// behavior), NOT poll. Failing to push means a poll-mode workspace
+// briefly attempts a real dispatch — visible failure (502 / SSRF
+// rejection / restart cascade), not a silent drop into activity_logs
+// where the agent might never look. Loud > silent, recoverable > lost.
+func TestProxyA2A_PollMode_FailsClosedToPush(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t) // empty Redis — forces resolveAgentURL DB lookup
+	broadcaster := newTestBroadcaster()
+	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
+
+	const wsID = "ws-mode-db-error"
+
+	expectBudgetCheck(mock, wsID)
+
+	// lookupDeliveryMode hits a transient DB error → must default push.
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs(wsID).
+		WillReturnError(sql.ErrConnDone)
+
+	// Push path proceeds to resolveAgentURL — empty result → 502 path.
+	mock.ExpectQuery("SELECT url, status FROM workspaces WHERE id =").
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"url", "status"}))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: wsID}}
+
+	body := `{"jsonrpc":"2.0","id":"x","method":"message/send","params":{}}`
+	c.Request = httptest.NewRequest("POST", "/workspaces/"+wsID+"/a2a", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.ProxyA2A(c)
+
+	if w.Code == http.StatusOK {
+		var resp map[string]interface{}
+		_ = json.Unmarshal(w.Body.Bytes(), &resp)
+		if resp["status"] == "queued" {
+			t.Errorf("DB error on delivery_mode lookup silently queued the request — must fail-closed-to-push, got body: %s", w.Body.String())
+		}
+	}
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet sqlmock expectations: %v", err)
+	}
+}
diff --git a/workspace-server/internal/handlers/handlers_additional_test.go b/workspace-server/internal/handlers/handlers_additional_test.go
index ca3df0de..7583493e 100644
--- a/workspace-server/internal/handlers/handlers_additional_test.go
+++ b/workspace-server/internal/handlers/handlers_additional_test.go
@@ -31,8 +31,9 @@ func TestWorkspaceCreate_WithParentID(t *testing.T) {
 	parentID := "parent-ws-123"
 	mock.ExpectBegin()
 	// Default tier is 3 (Privileged) — see workspace.go create-handler comment.
+	// delivery_mode defaults to "push" when payload omits it (#2339).
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs(sqlmock.AnyArg(), "Child Agent", nil, 3, "langgraph", sqlmock.AnyArg(), &parentID, nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks).
+		WithArgs(sqlmock.AnyArg(), "Child Agent", nil, 3, "langgraph", sqlmock.AnyArg(), &parentID, nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 	mock.ExpectCommit()
 	mock.ExpectExec("INSERT INTO canvas_layouts").
@@ -66,8 +67,9 @@ func TestWorkspaceCreate_ExplicitClaudeCodeRuntime(t *testing.T) {
 	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
 
 	mock.ExpectBegin()
+	// delivery_mode defaults to "push" when payload omits it (#2339).
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs(sqlmock.AnyArg(), "CC Agent", nil, 2, "claude-code", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks).
+		WithArgs(sqlmock.AnyArg(), "CC Agent", nil, 2, "claude-code", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 	mock.ExpectCommit()
 	mock.ExpectExec("INSERT INTO canvas_layouts").
@@ -288,7 +290,7 @@ func TestWorkspaceCreate_MaxConcurrentTasksOverride(t *testing.T) {
 
 	mock.ExpectBegin()
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs(sqlmock.AnyArg(), "Leader Agent", nil, 3, "claude-code", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), 3).
+		WithArgs(sqlmock.AnyArg(), "Leader Agent", nil, 3, "claude-code", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), 3, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 	mock.ExpectCommit()
 	mock.ExpectExec("INSERT INTO canvas_layouts").
@@ -320,8 +322,13 @@ func TestRegister_ProvisionerURLPreserved(t *testing.T) {
 	broadcaster := newTestBroadcaster()
 	handler := NewRegistryHandler(broadcaster)
 
+	// resolveDeliveryMode preflight — no row yet, default push (#2339).
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs("ws-prov").
+		WillReturnError(sql.ErrNoRows)
+
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs("ws-prov", "ws-prov", "http://localhost:8000", `{"name":"agent"}`).
+		WithArgs("ws-prov", "ws-prov", "http://localhost:8000", `{"name":"agent"}`, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 
 	// DB returns provisioner URL (127.0.0.1) — should take precedence over agent-reported URL
diff --git a/workspace-server/internal/handlers/handlers_test.go b/workspace-server/internal/handlers/handlers_test.go
index a051f662..435cff37 100644
--- a/workspace-server/internal/handlers/handlers_test.go
+++ b/workspace-server/internal/handlers/handlers_test.go
@@ -2,6 +2,7 @@ package handlers
 
 import (
 	"bytes"
+	"database/sql"
 	"encoding/json"
 	"fmt"
 	"net/http"
@@ -100,9 +101,14 @@ func TestRegisterHandler(t *testing.T) {
 	broadcaster := newTestBroadcaster()
 	handler := NewRegistryHandler(broadcaster)
 
+	// resolveDeliveryMode preflight — no row yet, default push (#2339).
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs("ws-123").
+		WillReturnError(sql.ErrNoRows)
+
 	// Expect the upsert INSERT ... ON CONFLICT
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs("ws-123", "ws-123", "http://localhost:8000", `{"name":"test"}`).
+		WithArgs("ws-123", "ws-123", "http://localhost:8000", `{"name":"test"}`, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 
 	// Expect the SELECT url query (for cache URL logic)
@@ -290,8 +296,9 @@ func TestWorkspaceCreate(t *testing.T) {
 
 	// Expect workspace INSERT (uuid is dynamic, use AnyArg for id, runtime, awareness_namespace).
 	// Default tier is 3 (Privileged) — see workspace.go create-handler comment.
+	// delivery_mode defaults to "push" when payload omits it (#2339).
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs(sqlmock.AnyArg(), "Test Agent", nil, 3, "langgraph", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks).
+		WithArgs(sqlmock.AnyArg(), "Test Agent", nil, 3, "langgraph", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 
 	// Expect transaction commit (no secrets in this payload)
diff --git a/workspace-server/internal/handlers/registry.go b/workspace-server/internal/handlers/registry.go
index 8bd694b8..60fe4b7d 100644
--- a/workspace-server/internal/handlers/registry.go
+++ b/workspace-server/internal/handlers/registry.go
@@ -2,6 +2,7 @@ package handlers
 
 import (
 	"context"
+	"database/sql"
 	"errors"
 	"fmt"
 	"log"
@@ -116,6 +117,41 @@ func (h *RegistryHandler) SetQueueDrainFunc(f QueueDrainFunc) {
 // returned IP is checked against the blocklist. This closes the gap where
 // an attacker could register agent.example.com pointing to 169.254.169.254.
 //
+// resolveDeliveryMode returns the EFFECTIVE delivery mode for a register
+// call given the payload's explicit value (which may be empty) and the
+// row's existing stored value (which may not exist yet on first
+// registration).
+//
+// Resolution order:
+//  1. payload value if non-empty (caller validated it's push/poll already)
+//  2. existing row's delivery_mode if the row exists
+//  3. "push" (the schema default — safe fallback for both new rows and
+//     a row whose delivery_mode is somehow NULL despite the NOT NULL
+//     CHECK constraint, which is forward-defensive only)
+//
+// Returns ("", err) only on a real DB error; sql.ErrNoRows is treated
+// as "no row yet, default to push" — that's the first-register flow.
+func (h *RegistryHandler) resolveDeliveryMode(ctx context.Context, workspaceID, payloadMode string) (string, error) {
+	if payloadMode != "" {
+		// Validated by IsValidDeliveryMode in the caller.
+		return payloadMode, nil
+	}
+	var existing sql.NullString
+	err := db.DB.QueryRowContext(ctx,
+		`SELECT delivery_mode FROM workspaces WHERE id = $1`, workspaceID,
+	).Scan(&existing)
+	if errors.Is(err, sql.ErrNoRows) {
+		return models.DeliveryModePush, nil
+	}
+	if err != nil {
+		return "", err
+	}
+	if existing.Valid && existing.String != "" {
+		return existing.String, nil
+	}
+	return models.DeliveryModePush, nil
+}
+
 // Returns a non-nil error suitable for including in a 400 Bad Request response.
 func validateAgentURL(rawURL string) error {
 	if rawURL == "" {
@@ -221,15 +257,11 @@ func (h *RegistryHandler) Register(c *gin.Context) {
 		return
 	}
 
-	// C6: reject SSRF-capable URLs before persisting or caching them.
-	if err := validateAgentURL(payload.URL); err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid request body"})
-		return
-	}
-
-	// C6: reject SSRF-capable URLs before persisting or caching them.
-	if err := validateAgentURL(payload.URL); err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+	// Validate explicit delivery_mode if the agent declared one; empty is
+	// allowed and resolves to the row's existing value (or "push" default)
+	// in the upsert below. See #2339 for the poll/push split rationale.
+	if payload.DeliveryMode != "" && !models.IsValidDeliveryMode(payload.DeliveryMode) {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "delivery_mode must be 'push' or 'poll'"})
 		return
 	}
 
@@ -250,9 +282,60 @@ func (h *RegistryHandler) Register(c *gin.Context) {
 		return // 401 response already written by requireWorkspaceToken
 	}
 
+	// Resolve the EFFECTIVE delivery mode for THIS register call: the
+	// payload's explicit value wins; falling back to the existing row's
+	// stored value; falling back to push (the schema default). Done AFTER
+	// the C18 token check so a hijack attempt fails on auth before we
+	// reveal whether a workspace row exists at all (resolveDeliveryMode
+	// would otherwise side-channel that via timing). #2339.
+	effectiveMode, err := h.resolveDeliveryMode(ctx, payload.ID, payload.DeliveryMode)
+	if err != nil {
+		log.Printf("Registry register: resolveDeliveryMode failed for %s: %v", payload.ID, err)
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "registration failed"})
+		return
+	}
+
+	// URL handling diverges by mode:
+	//   push: URL is required and must pass the SSRF safety check —
+	//     same as pre-#2339 behavior (the workspace must be reachable for
+	//     the proxy to dispatch).
+	//   poll: URL is optional and ignored when present. We don't even
+	//     validate it because the platform never dispatches to it. Skipping
+	//     validateAgentURL is intentional — a poll-mode workspace doesn't
+	//     need a publicly-routable URL, so a localhost / private IP /
+	//     missing URL is correct, not a mis-configuration.
+	if effectiveMode == models.DeliveryModePush {
+		if payload.URL == "" {
+			c.JSON(http.StatusBadRequest, gin.H{"error": "url is required for push-mode workspaces"})
+			return
+		}
+		if err := validateAgentURL(payload.URL); err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+			return
+		}
+	}
+
 	agentCardStr := string(payload.AgentCard)
 
-	// Upsert workspace: update url, agent_card, status if already exists.
+	// urlForUpsert: poll-mode workspaces don't need a URL. Empty input
+	// becomes NULL via sql.NullString so the row's URL stays clean (the
+	// CASE below also preserves an existing provisioner-set URL, which
+	// matters for hybrid setups where a workspace was previously push
+	// and is being re-registered as poll).
+	var urlForUpsert sql.NullString
+	if payload.URL != "" {
+		urlForUpsert = sql.NullString{String: payload.URL, Valid: true}
+	}
+
+	// modeForUpsert: empty payload value means "keep what's already on the
+	// row, or default to push for new rows". The COALESCE in the CASE on
+	// the UPDATE branch and the EXCLUDED.delivery_mode on the INSERT branch
+	// implement that. We pass effectiveMode (already resolved above) so
+	// the row's mode is consistent with the URL-validation decision we
+	// just made.
+	modeForUpsert := effectiveMode
+
+	// Upsert workspace: update url, agent_card, status, delivery_mode if already exists.
 	// On INSERT (workspace not yet created via POST /workspaces), use ID as name placeholder.
 	// Keep existing URL if provisioner already set a host-accessible one (starts with http://127.0.0.1).
 	//
@@ -261,9 +344,9 @@ func (h *RegistryHandler) Register(c *gin.Context) {
 	// the row. Without this guard, bulk deletes left tier-3 stragglers because
 	// the last pre-teardown heartbeat flipped status back to 'online' after
 	// Delete's UPDATE.
-	_, err := db.DB.ExecContext(ctx, `
-		INSERT INTO workspaces (id, name, url, agent_card, status, last_heartbeat_at)
-		VALUES ($1, $2, $3, $4::jsonb, 'online', now())
+	_, err = db.DB.ExecContext(ctx, `
+		INSERT INTO workspaces (id, name, url, agent_card, status, last_heartbeat_at, delivery_mode)
+		VALUES ($1, $2, $3, $4::jsonb, 'online', now(), $5)
 		ON CONFLICT (id) DO UPDATE SET
 			url = CASE
 				WHEN workspaces.url LIKE 'http://127.0.0.1%' THEN workspaces.url
@@ -272,9 +355,10 @@ func (h *RegistryHandler) Register(c *gin.Context) {
 			agent_card = EXCLUDED.agent_card,
 			status = 'online',
 			last_heartbeat_at = now(),
+			delivery_mode = EXCLUDED.delivery_mode,
 			updated_at = now()
 		WHERE workspaces.status IS DISTINCT FROM 'removed'
-	`, payload.ID, payload.ID, payload.URL, agentCardStr)
+	`, payload.ID, payload.ID, urlForUpsert, agentCardStr, modeForUpsert)
 	if err != nil {
 		log.Printf("Registry register error: %v (id=%s)", err, payload.ID)
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "registration failed"})
@@ -289,6 +373,12 @@ func (h *RegistryHandler) Register(c *gin.Context) {
 	// Cache URL — prefer existing provisioner URL over agent-reported one.
 	// The DB CASE already preserves provisioner URLs, so read from DB as source of truth
 	// instead of adding a Redis round-trip on every registration.
+	//
+	// Poll-mode workspaces typically have no URL at all; skip the cache
+	// writes entirely in that case so we don't poison the cache with an
+	// empty string that another caller might mistake for "registered with
+	// no URL" vs "not yet registered". The proxy short-circuits poll-mode
+	// before consulting the URL cache anyway (see #2339 PR 2).
 	cachedURL := payload.URL
 	var dbURL string
 	if err := db.DB.QueryRowContext(ctx, `SELECT url FROM workspaces WHERE id = $1`, payload.ID).Scan(&dbURL); err == nil {
@@ -296,20 +386,26 @@ func (h *RegistryHandler) Register(c *gin.Context) {
 			cachedURL = dbURL
 		}
 	}
-	if err := db.CacheURL(ctx, payload.ID, cachedURL); err != nil {
-		log.Printf("Registry cache url error: %v", err)
+	if cachedURL != "" {
+		if err := db.CacheURL(ctx, payload.ID, cachedURL); err != nil {
+			log.Printf("Registry cache url error: %v", err)
+		}
 	}
 
 	// Cache agent-reported URL separately for workspace-to-workspace discovery
-	// (Docker containers can reach each other by hostname but not via host ports)
-	if err := db.CacheInternalURL(ctx, payload.ID, payload.URL); err != nil {
-		log.Printf("Registry cache internal url error: %v", err)
+	// (Docker containers can reach each other by hostname but not via host ports).
+	// Same skip-when-empty rule as above.
+	if payload.URL != "" {
+		if err := db.CacheInternalURL(ctx, payload.ID, payload.URL); err != nil {
+			log.Printf("Registry cache internal url error: %v", err)
+		}
 	}
 
 	// Broadcast WORKSPACE_ONLINE
 	if err := h.broadcaster.RecordAndBroadcast(ctx, "WORKSPACE_ONLINE", payload.ID, map[string]interface{}{
-		"url":        cachedURL,
-		"agent_card": payload.AgentCard,
+		"url":           cachedURL,
+		"agent_card":    payload.AgentCard,
+		"delivery_mode": effectiveMode,
 	}); err != nil {
 		log.Printf("Registry broadcast error: %v", err)
 	}
@@ -324,7 +420,7 @@ func (h *RegistryHandler) Register(c *gin.Context) {
 	// Legacy workspaces that registered before tokens existed have no
 	// live token; they bootstrap one here on their next register call.
 	// New workspaces always pass through this path on their first boot.
-	response := gin.H{"status": "registered"}
+	response := gin.H{"status": "registered", "delivery_mode": effectiveMode}
 	if hasLive, hasLiveErr := wsauth.HasAnyLiveToken(ctx, db.DB, payload.ID); hasLiveErr == nil && !hasLive {
 		token, tokErr := wsauth.IssueToken(ctx, db.DB, payload.ID)
 		if tokErr != nil {
diff --git a/workspace-server/internal/handlers/registry_test.go b/workspace-server/internal/handlers/registry_test.go
index 645dd924..5ad4fc62 100644
--- a/workspace-server/internal/handlers/registry_test.go
+++ b/workspace-server/internal/handlers/registry_test.go
@@ -61,9 +61,17 @@ func TestRegister_DBError(t *testing.T) {
 	broadcaster := newTestBroadcaster()
 	handler := NewRegistryHandler(broadcaster)
 
+	// resolveDeliveryMode SELECT — no row yet, so default "push".
+	// (#2339) New preflight after C18 token check; HasAnyLiveToken's COUNT
+	// query has no mock here and fails-open per requireWorkspaceToken's
+	// DB-error handling, so the next DB hit is this delivery_mode lookup.
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs("ws-fail").
+		WillReturnError(sql.ErrNoRows)
+
 	// DB insert fails
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs("ws-fail", "ws-fail", "http://localhost:8000", `{"name":"test"}`).
+		WithArgs("ws-fail", "ws-fail", "http://localhost:8000", `{"name":"test"}`, "push").
 		WillReturnError(sql.ErrConnDone)
 
 	w := httptest.NewRecorder()
@@ -579,10 +587,14 @@ func TestRegister_GuardAgainstResurrectingRemovedRow(t *testing.T) {
 	broadcaster := newTestBroadcaster()
 	handler := NewRegistryHandler(broadcaster)
 
+	// resolveDeliveryMode preflight — no row yet, default push (#2339).
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs("ws-resurrect").
+		WillReturnError(sql.ErrNoRows)
 	// This regex-ish match requires the guard. If the handler ever drops
 	// the clause the test fails because the emitted SQL won't match.
 	mock.ExpectExec("ON CONFLICT.*WHERE workspaces.status IS DISTINCT FROM 'removed'").
-		WithArgs("ws-resurrect", "ws-resurrect", "http://localhost:8000", `{"name":"x"}`).
+		WithArgs("ws-resurrect", "ws-resurrect", "http://localhost:8000", `{"name":"x"}`, "push").
 		WillReturnResult(sqlmock.NewResult(0, 0)) // 0 rows affected = correctly guarded
 	mock.ExpectQuery("SELECT url FROM workspaces WHERE id").
 		WithArgs("ws-resurrect").
@@ -843,9 +855,14 @@ func TestRegister_C18_BootstrapAllowedNoTokens(t *testing.T) {
 		WithArgs("ws-new").
 		WillReturnRows(sqlmock.NewRows([]string{"count"}).AddRow(0))
 
+	// resolveDeliveryMode — no row yet, default push (#2339).
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs("ws-new").
+		WillReturnError(sql.ErrNoRows)
+
 	// Workspace upsert proceeds normally.
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs("ws-new", "ws-new", "http://localhost:9100", `{"name":"new-agent"}`).
+		WithArgs("ws-new", "ws-new", "http://localhost:9100", `{"name":"new-agent"}`, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 
 	mock.ExpectQuery("SELECT url FROM workspaces WHERE id").
@@ -910,6 +927,11 @@ func TestRegister_ReturnsPlatformInboundSecret_RFC2312_PRF(t *testing.T) {
 		WithArgs(wsID).
 		WillReturnRows(sqlmock.NewRows([]string{"count"}).AddRow(0))
 
+	// resolveDeliveryMode — no row yet, default push (#2339).
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs(wsID).
+		WillReturnError(sql.ErrNoRows)
+
 	// Workspace upsert.
 	mock.ExpectExec("INSERT INTO workspaces").
 		WillReturnResult(sqlmock.NewResult(0, 1))
@@ -980,6 +1002,10 @@ func TestRegister_NoInboundSecret_OmitsField(t *testing.T) {
 	mock.ExpectQuery("SELECT COUNT\\(\\*\\) FROM workspace_auth_tokens").
 		WithArgs(wsID).
 		WillReturnRows(sqlmock.NewRows([]string{"count"}).AddRow(0))
+	// resolveDeliveryMode — no row yet, default push (#2339).
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs(wsID).
+		WillReturnError(sql.ErrNoRows)
 	mock.ExpectExec("INSERT INTO workspaces").WillReturnResult(sqlmock.NewResult(0, 1))
 	mock.ExpectQuery("SELECT url FROM workspaces WHERE id").
 		WithArgs(wsID).
@@ -1063,9 +1089,14 @@ func TestRegister_DBErrorResponseIsOpaque(t *testing.T) {
 		WithArgs("ws-errtest").
 		WillReturnRows(sqlmock.NewRows([]string{"count"}).AddRow(0))
 
+	// resolveDeliveryMode — no row yet, default push (#2339).
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs("ws-errtest").
+		WillReturnError(sql.ErrNoRows)
+
 	// DB upsert fails with a descriptive internal error.
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs("ws-errtest", "ws-errtest", "http://localhost:9200", `{"name":"err-agent"}`).
+		WithArgs("ws-errtest", "ws-errtest", "http://localhost:9200", `{"name":"err-agent"}`, "push").
 		WillReturnError(sql.ErrConnDone)
 
 	w := httptest.NewRecorder()
@@ -1283,3 +1314,211 @@ func TestHeartbeat_MonthlySpend_Zero_NoUpdate(t *testing.T) {
 		t.Errorf("monthly_spend=0 must not trigger a DB write for spend: %v", err)
 	}
 }
+
+// ==================== Register — delivery_mode (#2339) ====================
+
+// TestRegister_PollMode_AcceptsEmptyURL verifies the new contract:
+// when delivery_mode=poll, URL is optional. A poll-mode workspace
+// (e.g. operator's laptop running molecule-mcp-claude-channel) has
+// no public URL to register, and we must NOT reject the registration
+// for that. The proxy short-circuits poll-mode A2A in PR 2 — no URL
+// needed there either.
+func TestRegister_PollMode_AcceptsEmptyURL(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewRegistryHandler(broadcaster)
+
+	const wsID = "ws-poll-no-url"
+
+	// Bootstrap path — no live tokens, so requireWorkspaceToken passes
+	// without an Authorization header.
+	mock.ExpectQuery("SELECT COUNT\\(\\*\\) FROM workspace_auth_tokens").
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"count"}).AddRow(0))
+
+	// resolveDeliveryMode: payload sets "poll" explicitly, so we should
+	// NOT hit the DB lookup at all (the helper short-circuits when
+	// payload value is non-empty). Asserted by the absence of an
+	// ExpectQuery for SELECT delivery_mode here.
+
+	// Upsert MUST run with empty URL (sql.NullString) and delivery_mode=poll.
+	mock.ExpectExec("INSERT INTO workspaces").
+		WithArgs(wsID, wsID, sql.NullString{}, `{"name":"poll-agent"}`, "poll").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	// SELECT url for cache: returns NULL/empty for poll-mode rows. The
+	// handler skips the cache writes in that case (no CacheURL /
+	// CacheInternalURL expectations).
+	mock.ExpectQuery("SELECT url FROM workspaces WHERE id").
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"url"}).AddRow(""))
+
+	mock.ExpectExec("INSERT INTO structure_events").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	// Token issuance — first-register path.
+	mock.ExpectQuery("SELECT COUNT\\(\\*\\) FROM workspace_auth_tokens").
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"count"}).AddRow(0))
+	mock.ExpectExec("INSERT INTO workspace_auth_tokens").
+		WillReturnResult(sqlmock.NewResult(1, 1))
+	mock.ExpectQuery(`SELECT platform_inbound_secret FROM workspaces WHERE id = \$1`).
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"platform_inbound_secret"}).AddRow(nil))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest("POST", "/registry/register",
+		bytes.NewBufferString(`{"id":"`+wsID+`","delivery_mode":"poll","agent_card":{"name":"poll-agent"}}`))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Register(c)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("poll-mode + empty URL: expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+
+	var resp map[string]interface{}
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("response is not valid JSON: %v", err)
+	}
+	if resp["delivery_mode"] != "poll" {
+		t.Errorf("response.delivery_mode = %v, want %q", resp["delivery_mode"], "poll")
+	}
+	// First-register must still mint a token regardless of delivery_mode.
+	if resp["auth_token"] == nil {
+		t.Error("expected auth_token in response (first-register path)")
+	}
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet expectations: %v", err)
+	}
+}
+
+// TestRegister_PushMode_RejectsEmptyURL verifies the symmetric contract:
+// push-mode (the default) still requires a URL. Skipping URL validation
+// in poll-mode mustn't accidentally relax the push-mode invariant — that
+// would silently break dispatch for the rest of the fleet.
+func TestRegister_PushMode_RejectsEmptyURL(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewRegistryHandler(broadcaster)
+
+	// Bootstrap path through requireWorkspaceToken.
+	mock.ExpectQuery("SELECT COUNT\\(\\*\\) FROM workspace_auth_tokens").
+		WithArgs("ws-push-no-url").
+		WillReturnRows(sqlmock.NewRows([]string{"count"}).AddRow(0))
+
+	// resolveDeliveryMode: no row yet, defaults to push. The handler
+	// then validates the URL — which is empty — and returns 400.
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs("ws-push-no-url").
+		WillReturnError(sql.ErrNoRows)
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest("POST", "/registry/register",
+		bytes.NewBufferString(`{"id":"ws-push-no-url","agent_card":{"name":"push-agent"}}`))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Register(c)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("push-mode + empty URL: expected 400, got %d: %s", w.Code, w.Body.String())
+	}
+	if !strings.Contains(w.Body.String(), "url is required") {
+		t.Errorf("expected 'url is required' in error body, got: %s", w.Body.String())
+	}
+}
+
+// TestRegister_InvalidDeliveryMode rejects payloads that declare an
+// unrecognised delivery_mode — defends against a typo silently
+// becoming "push" and leaving the operator wondering why polling
+// doesn't work.
+func TestRegister_InvalidDeliveryMode(t *testing.T) {
+	setupTestDB(t)
+	setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewRegistryHandler(broadcaster)
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest("POST", "/registry/register",
+		bytes.NewBufferString(`{"id":"ws-x","url":"http://localhost:8000","agent_card":{"name":"a"},"delivery_mode":"webhook"}`))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Register(c)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("invalid delivery_mode: expected 400, got %d: %s", w.Code, w.Body.String())
+	}
+	if !strings.Contains(w.Body.String(), "delivery_mode") {
+		t.Errorf("expected error body to mention delivery_mode, got: %s", w.Body.String())
+	}
+}
+
+// TestRegister_PollMode_PreservesExistingValue: when the row already
+// has delivery_mode=poll and the payload doesn't set it, the resolved
+// mode should be poll — i.e. "absent payload mode" must NOT silently
+// downgrade an existing poll workspace to push. Ensures Telegram-style
+// stability: mode is sticky once set.
+func TestRegister_PollMode_PreservesExistingValue(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewRegistryHandler(broadcaster)
+
+	const wsID = "ws-existing-poll"
+
+	mock.ExpectQuery("SELECT COUNT\\(\\*\\) FROM workspace_auth_tokens").
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"count"}).AddRow(0))
+
+	// resolveDeliveryMode: row exists with delivery_mode=poll.
+	mock.ExpectQuery("SELECT delivery_mode FROM workspaces WHERE id").
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"delivery_mode"}).AddRow("poll"))
+
+	// Upsert carries the resolved poll mode forward — even though
+	// payload didn't restate it. URL still empty (poll-mode shape).
+	mock.ExpectExec("INSERT INTO workspaces").
+		WithArgs(wsID, wsID, sql.NullString{}, `{"name":"a"}`, "poll").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectQuery("SELECT url FROM workspaces WHERE id").
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"url"}).AddRow(""))
+	mock.ExpectExec("INSERT INTO structure_events").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectQuery("SELECT COUNT\\(\\*\\) FROM workspace_auth_tokens").
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"count"}).AddRow(0))
+	mock.ExpectExec("INSERT INTO workspace_auth_tokens").
+		WillReturnResult(sqlmock.NewResult(1, 1))
+	mock.ExpectQuery(`SELECT platform_inbound_secret FROM workspaces WHERE id = \$1`).
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"platform_inbound_secret"}).AddRow(nil))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	// No delivery_mode in payload — must inherit "poll" from the row.
+	c.Request = httptest.NewRequest("POST", "/registry/register",
+		bytes.NewBufferString(`{"id":"`+wsID+`","agent_card":{"name":"a"}}`))
+	c.Request.Header.Set("Content-Type", "application/json")
+
+	handler.Register(c)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+	var resp map[string]interface{}
+	_ = json.Unmarshal(w.Body.Bytes(), &resp)
+	if resp["delivery_mode"] != "poll" {
+		t.Errorf("delivery_mode = %v, want %q (must inherit existing row's mode when payload absent)",
+			resp["delivery_mode"], "poll")
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet expectations: %v", err)
+	}
+}
diff --git a/workspace-server/internal/handlers/workspace.go b/workspace-server/internal/handlers/workspace.go
index 00d86b7e..ae70256b 100644
--- a/workspace-server/internal/handlers/workspace.go
+++ b/workspace-server/internal/handlers/workspace.go
@@ -224,11 +224,24 @@ func (h *WorkspaceHandler) Create(c *gin.Context) {
 	if maxConcurrent <= 0 {
 		maxConcurrent = models.DefaultMaxConcurrentTasks
 	}
-	// Insert workspace with runtime persisted in DB (inside transaction)
+	// delivery_mode: explicit payload value (validated below), else default
+	// to push (the schema default + pre-#2339 behavior). Validated here, not
+	// in workspace_provision.go, so a bad value fails the create cleanly
+	// instead of mid-provision after side effects.
+	deliveryMode := payload.DeliveryMode
+	if deliveryMode == "" {
+		deliveryMode = models.DeliveryModePush
+	}
+	if !models.IsValidDeliveryMode(deliveryMode) {
+		tx.Rollback() //nolint:errcheck
+		c.JSON(http.StatusBadRequest, gin.H{"error": "delivery_mode must be 'push' or 'poll'"})
+		return
+	}
+	// Insert workspace with runtime + delivery_mode persisted in DB (inside transaction)
 	_, err := tx.ExecContext(ctx, `
-		INSERT INTO workspaces (id, name, role, tier, runtime, awareness_namespace, status, parent_id, workspace_dir, workspace_access, budget_limit, max_concurrent_tasks)
-		VALUES ($1, $2, $3, $4, $5, $6, 'provisioning', $7, $8, $9, $10, $11)
-	`, id, payload.Name, role, payload.Tier, payload.Runtime, awarenessNamespace, payload.ParentID, workspaceDir, workspaceAccess, payload.BudgetLimit, maxConcurrent)
+		INSERT INTO workspaces (id, name, role, tier, runtime, awareness_namespace, status, parent_id, workspace_dir, workspace_access, budget_limit, max_concurrent_tasks, delivery_mode)
+		VALUES ($1, $2, $3, $4, $5, $6, 'provisioning', $7, $8, $9, $10, $11, $12)
+	`, id, payload.Name, role, payload.Tier, payload.Runtime, awarenessNamespace, payload.ParentID, workspaceDir, workspaceAccess, payload.BudgetLimit, maxConcurrent, deliveryMode)
 	if err != nil {
 		tx.Rollback() //nolint:errcheck
 		log.Printf("Create workspace error: %v", err)
diff --git a/workspace-server/internal/handlers/workspace_budget_test.go b/workspace-server/internal/handlers/workspace_budget_test.go
index b38e984b..920dad9c 100644
--- a/workspace-server/internal/handlers/workspace_budget_test.go
+++ b/workspace-server/internal/handlers/workspace_budget_test.go
@@ -152,6 +152,7 @@ func TestWorkspaceBudget_Create_WithLimit(t *testing.T) {
 			"none",           // workspace_access
 			&budgetVal,       // budget_limit ($10)
 			models.DefaultMaxConcurrentTasks, // max_concurrent_tasks default
+			"push",           // delivery_mode default (#2339)
 		).
 		WillReturnResult(sqlmock.NewResult(0, 1))
 	mock.ExpectCommit()
diff --git a/workspace-server/internal/handlers/workspace_test.go b/workspace-server/internal/handlers/workspace_test.go
index 43faa8f9..8afc93e8 100644
--- a/workspace-server/internal/handlers/workspace_test.go
+++ b/workspace-server/internal/handlers/workspace_test.go
@@ -155,7 +155,7 @@ func TestWorkspaceCreate_DBInsertError(t *testing.T) {
 	// Transaction begins, workspace INSERT fails, transaction is rolled back.
 	mock.ExpectBegin()
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs(sqlmock.AnyArg(), "Failing Agent", nil, 3, "langgraph", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks).
+		WithArgs(sqlmock.AnyArg(), "Failing Agent", nil, 3, "langgraph", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks, "push").
 		WillReturnError(sql.ErrConnDone)
 	mock.ExpectRollback()
 
@@ -188,7 +188,7 @@ func TestWorkspaceCreate_DefaultsApplied(t *testing.T) {
 	// Expect workspace INSERT with defaulted tier=3 (Privileged — the
 	// handler default in workspace.go), runtime="langgraph"
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs(sqlmock.AnyArg(), "Default Agent", nil, 3, "langgraph", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks).
+		WithArgs(sqlmock.AnyArg(), "Default Agent", nil, 3, "langgraph", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 	mock.ExpectCommit()
 
@@ -239,7 +239,7 @@ func TestWorkspaceCreate_WithSecrets_Persists(t *testing.T) {
 
 	mock.ExpectBegin()
 	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs(sqlmock.AnyArg(), "Hermes Agent", nil, 3, "hermes", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks).
+		WithArgs(sqlmock.AnyArg(), "Hermes Agent", nil, 3, "hermes", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 	// Secret inserted inside the same transaction.
 	mock.ExpectExec("INSERT INTO workspace_secrets").
@@ -1258,7 +1258,7 @@ runtime_config:
 	mock.ExpectExec("INSERT INTO workspaces").
 		WithArgs(
 			sqlmock.AnyArg(), "Hermes Agent", nil, 3, "hermes",
-			sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks).
+			sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 	mock.ExpectCommit()
 	mock.ExpectExec("INSERT INTO canvas_layouts").
@@ -1315,7 +1315,7 @@ model: anthropic:claude-sonnet-4-5
 	mock.ExpectExec("INSERT INTO workspaces").
 		WithArgs(
 			sqlmock.AnyArg(), "Legacy Agent", nil, 3, "langgraph",
-			sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks).
+			sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 	mock.ExpectCommit()
 	mock.ExpectExec("INSERT INTO canvas_layouts").
@@ -1368,7 +1368,7 @@ runtime_config:
 	mock.ExpectExec("INSERT INTO workspaces").
 		WithArgs(
 			sqlmock.AnyArg(), "Custom Hermes", nil, 3, "hermes",
-			sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks).
+			sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks, "push").
 		WillReturnResult(sqlmock.NewResult(0, 1))
 	mock.ExpectCommit()
 	mock.ExpectExec("INSERT INTO canvas_layouts").
diff --git a/workspace-server/internal/models/architecture_test.go b/workspace-server/internal/models/architecture_test.go
new file mode 100644
index 00000000..40b65ba6
--- /dev/null
+++ b/workspace-server/internal/models/architecture_test.go
@@ -0,0 +1,63 @@
+package models_test
+
+// Architecture test (#2344): models is a leaf — it carries pure type
+// definitions and must not import any other internal/* package. Almost
+// every package in workspace-server depends on models; if models grew a
+// reverse dep, the import graph would cycle.
+//
+// If this test fails: you put behavior inside models. Move the behavior
+// to whichever package actually owns it (handlers, provisioner, db, …)
+// and have *that* package import models, not the reverse.
+
+import (
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const moduleInternalPrefix = "github.com/Molecule-AI/molecule-monorepo/platform/internal/"
+
+func TestModelsHasNoInternalDependencies(t *testing.T) {
+	t.Parallel()
+	for path, file := range listImports(t, ".") {
+		if strings.HasPrefix(path, moduleInternalPrefix) {
+			t.Errorf(
+				"models must not import other internal packages "+
+					"(found %q in %s) — models is the pure-types leaf and any "+
+					"reverse dep creates an import cycle since most packages "+
+					"depend on models. See workspace-server/internal/models/architecture_test.go.",
+				path, file,
+			)
+		}
+	}
+}
+
+func listImports(t *testing.T, dir string) map[string]string {
+	t.Helper()
+	fset := token.NewFileSet()
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		t.Fatalf("read %s: %v", dir, err)
+	}
+	out := make(map[string]string)
+	for _, e := range entries {
+		name := e.Name()
+		if e.IsDir() || !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {
+			continue
+		}
+		f, err := parser.ParseFile(fset, filepath.Join(dir, name), nil, parser.ImportsOnly)
+		if err != nil {
+			t.Fatalf("parse %s: %v", name, err)
+		}
+		for _, imp := range f.Imports {
+			path := strings.Trim(imp.Path.Value, "\"")
+			if _, seen := out[path]; !seen {
+				out[path] = name
+			}
+		}
+	}
+	return out
+}
diff --git a/workspace-server/internal/models/workspace.go b/workspace-server/internal/models/workspace.go
index e8850425..11284473 100644
--- a/workspace-server/internal/models/workspace.go
+++ b/workspace-server/internal/models/workspace.go
@@ -32,16 +32,42 @@ type Workspace struct {
 	UptimeSeconds      int             `json:"uptime_seconds" db:"uptime_seconds"`
 	CreatedAt          time.Time       `json:"created_at" db:"created_at"`
 	UpdatedAt          time.Time       `json:"updated_at" db:"updated_at"`
+	// DeliveryMode: "push" (synchronous to URL — default) or "poll" (logged
+	// to activity_logs, agent reads via GET /activity?since_id=). See
+	// migration 045 + RFC #2339.
+	DeliveryMode       string          `json:"delivery_mode" db:"delivery_mode"`
 	// Canvas layout fields (from JOIN)
 	X         float64 `json:"x"`
 	Y         float64 `json:"y"`
 	Collapsed bool    `json:"collapsed"`
 }
 
+// Delivery mode constants. Matches the CHECK constraint in migration 045.
+const (
+	DeliveryModePush = "push"
+	DeliveryModePoll = "poll"
+)
+
+// IsValidDeliveryMode reports whether s is one of the recognised
+// delivery modes. Empty string is NOT valid here — callers must
+// resolve the default ("push") before calling.
+func IsValidDeliveryMode(s string) bool {
+	return s == DeliveryModePush || s == DeliveryModePoll
+}
+
 type RegisterPayload struct {
-	ID        string          `json:"id" binding:"required"`
-	URL       string          `json:"url" binding:"required"`
-	AgentCard json.RawMessage `json:"agent_card" binding:"required"`
+	ID string `json:"id" binding:"required"`
+	// URL is required for push-mode workspaces; optional / unused for
+	// poll-mode (the platform never dispatches to it). The handler
+	// enforces the conditional requirement based on the resolved
+	// delivery mode (payload value, falling back to the row's existing
+	// value, falling back to "push").
+	URL          string          `json:"url"`
+	AgentCard    json.RawMessage `json:"agent_card" binding:"required"`
+	// DeliveryMode is optional. Empty string means "keep the existing
+	// value on the workspace row, or default to push for new rows".
+	// When set, must be one of DeliveryModePush / DeliveryModePoll.
+	DeliveryMode string          `json:"delivery_mode,omitempty"`
 }
 
 type HeartbeatPayload struct {
@@ -127,7 +153,11 @@ type CreateWorkspacePayload struct {
 	Model    string  `json:"model"`
 	Runtime      string  `json:"runtime"`       // "langgraph" (default), "claude-code", etc.
 	External     bool    `json:"external"`      // true = no Docker container, just a registered URL
-	URL          string  `json:"url"`           // for external workspaces: the A2A endpoint URL
+	URL          string  `json:"url"`           // for external workspaces: the A2A endpoint URL (push mode only — omit for poll)
+	// DeliveryMode: "push" (default) sends inbound A2A to URL synchronously;
+	// "poll" records inbound to activity_logs for the agent to consume via
+	// GET /activity?since_id=. Poll mode does not require a URL. See #2339.
+	DeliveryMode string  `json:"delivery_mode,omitempty"`
 	WorkspaceDir    string  `json:"workspace_dir"`    // host path to mount as /workspace (empty = isolated volume)
 	WorkspaceAccess string  `json:"workspace_access"` // "none" (default), "read_only", or "read_write" — see #65
 	ParentID        *string `json:"parent_id"`
diff --git a/workspace-server/internal/provisioner/architecture_test.go b/workspace-server/internal/provisioner/architecture_test.go
new file mode 100644
index 00000000..c7455e52
--- /dev/null
+++ b/workspace-server/internal/provisioner/architecture_test.go
@@ -0,0 +1,80 @@
+package provisioner_test
+
+// Architecture test (#2344): provisioner is below handlers/router in
+// the layer hierarchy. handlers wires provisioner into HTTP routes;
+// the reverse direction (provisioner reaching back into handlers or
+// the router) creates a cycle and tangles infra-orchestration with
+// transport.
+//
+// Note: provisioner CURRENTLY imports db (for the runtime-image
+// lookup). That's a known coupling — see PR #2276 review thread on
+// where image resolution should live. The narrower rule we enforce
+// here is "no upward import to handlers/router," which is the harder
+// rule to keep clean.
+//
+// If this test fails: you reached "up" the stack. Pass whatever you
+// need from handlers down through a constructor parameter or a
+// function-typed callback instead of importing the package directly.
+
+import (
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const moduleInternalPrefix = "github.com/Molecule-AI/molecule-monorepo/platform/internal/"
+
+var provisionerForbiddenImports = []string{
+	moduleInternalPrefix + "handlers",
+	moduleInternalPrefix + "router",
+}
+
+func TestProvisionerDoesNotImportUpstreamLayers(t *testing.T) {
+	t.Parallel()
+	imports := listImports(t, ".")
+	for path, file := range imports {
+		for _, forbidden := range provisionerForbiddenImports {
+			if path == forbidden || strings.HasPrefix(path, forbidden+"/") {
+				t.Errorf(
+					"provisioner must not import %q (found in %s) — "+
+						"provisioner sits below handlers/router in the layer "+
+						"hierarchy and a reverse dep creates a cycle. Pass "+
+						"what you need down via constructor params or "+
+						"function-typed callbacks. See workspace-server/internal/"+
+						"provisioner/architecture_test.go.",
+					path, file,
+				)
+			}
+		}
+	}
+}
+
+func listImports(t *testing.T, dir string) map[string]string {
+	t.Helper()
+	fset := token.NewFileSet()
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		t.Fatalf("read %s: %v", dir, err)
+	}
+	out := make(map[string]string)
+	for _, e := range entries {
+		name := e.Name()
+		if e.IsDir() || !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {
+			continue
+		}
+		f, err := parser.ParseFile(fset, filepath.Join(dir, name), nil, parser.ImportsOnly)
+		if err != nil {
+			t.Fatalf("parse %s: %v", name, err)
+		}
+		for _, imp := range f.Imports {
+			path := strings.Trim(imp.Path.Value, "\"")
+			if _, seen := out[path]; !seen {
+				out[path] = name
+			}
+		}
+	}
+	return out
+}
diff --git a/workspace-server/internal/wsauth/architecture_test.go b/workspace-server/internal/wsauth/architecture_test.go
new file mode 100644
index 00000000..c61e5b7e
--- /dev/null
+++ b/workspace-server/internal/wsauth/architecture_test.go
@@ -0,0 +1,68 @@
+package wsauth_test
+
+// Architecture test (#2344): wsauth is a leaf package — it must not import
+// any other internal/* package. The auth layer is below business logic;
+// importing handlers, db, or any cousin package would force every wsauth
+// test to spin up that subsystem, defeating the unit-test boundary that
+// makes the auth code reviewable.
+//
+// If this test fails: you added an import that crosses a layer. Either
+// move the dependency the other direction (consumer wires wsauth into
+// itself), accept the boundary by inlining what you need, or — if the
+// new coupling is genuinely correct — explicitly update this test with
+// the new allowed import + a comment explaining why.
+
+import (
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const moduleInternalPrefix = "github.com/Molecule-AI/molecule-monorepo/platform/internal/"
+
+func TestWsauthHasNoInternalDependencies(t *testing.T) {
+	t.Parallel()
+	for path, file := range listImports(t, ".") {
+		if strings.HasPrefix(path, moduleInternalPrefix) {
+			t.Errorf(
+				"wsauth must not import other internal packages "+
+					"(found %q in %s) — wsauth is the auth leaf and must stay "+
+					"unit-testable without spinning up other subsystems. "+
+					"See workspace-server/internal/wsauth/architecture_test.go for context.",
+				path, file,
+			)
+		}
+	}
+}
+
+// listImports returns import-path → first-file-where-seen for non-test
+// .go files in dir. Used by every architecture_test.go in this tree.
+func listImports(t *testing.T, dir string) map[string]string {
+	t.Helper()
+	fset := token.NewFileSet()
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		t.Fatalf("read %s: %v", dir, err)
+	}
+	out := make(map[string]string)
+	for _, e := range entries {
+		name := e.Name()
+		if e.IsDir() || !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {
+			continue
+		}
+		f, err := parser.ParseFile(fset, filepath.Join(dir, name), nil, parser.ImportsOnly)
+		if err != nil {
+			t.Fatalf("parse %s: %v", name, err)
+		}
+		for _, imp := range f.Imports {
+			path := strings.Trim(imp.Path.Value, "\"")
+			if _, seen := out[path]; !seen {
+				out[path] = name
+			}
+		}
+	}
+	return out
+}
diff --git a/workspace-server/migrations/045_workspaces_delivery_mode.down.sql b/workspace-server/migrations/045_workspaces_delivery_mode.down.sql
new file mode 100644
index 00000000..2d21840e
--- /dev/null
+++ b/workspace-server/migrations/045_workspaces_delivery_mode.down.sql
@@ -0,0 +1,8 @@
+-- 045_workspaces_delivery_mode.down.sql
+--
+-- Drops the delivery_mode column. Any code reading it after rollback falls
+-- back to push mode (the pre-#2339 behavior), so this is forward-only-safe
+-- only if the matching application code is rolled back in the same release.
+
+ALTER TABLE workspaces
+    DROP COLUMN IF EXISTS delivery_mode;
diff --git a/workspace-server/migrations/045_workspaces_delivery_mode.up.sql b/workspace-server/migrations/045_workspaces_delivery_mode.up.sql
new file mode 100644
index 00000000..1eab5e84
--- /dev/null
+++ b/workspace-server/migrations/045_workspaces_delivery_mode.up.sql
@@ -0,0 +1,54 @@
+-- 045_workspaces_delivery_mode.up.sql
+--
+-- Per-workspace declaration of how A2A traffic is delivered TO the workspace.
+--
+--   push (default, today's behavior)
+--     Platform synchronously POSTs to workspaces.url and surfaces the response
+--     to the caller. Requires a publicly-routable URL (SSRF gate at
+--     a2a_proxy.go:455). Used by all hosted runtimes (claude-code, hermes,
+--     etc.) where the platform's provisioner sets the URL at boot.
+--
+--   poll
+--     Platform records the inbound A2A as an a2a_receive activity row and
+--     returns 200 to the caller without dispatching. The agent client (e.g.
+--     molecule-mcp-claude-channel) consumes the inbox via
+--     GET /workspaces/:id/activity?since_id=… and replies via
+--     POST /workspaces/:peer/a2a. NO URL required — works through every NAT,
+--     firewall, and dev-laptop without a tunnel.
+--
+-- Why a column and not a derived signal:
+--
+--   * Mutual exclusivity matches Telegram's getUpdates / setWebhook
+--     semantics — operationally cleaner than "both half-work because URL
+--     is empty". Telegram explicitly rejects double-delivery; we now do
+--     the same.
+--   * The platform short-circuits BEFORE the SSRF check, so a poll-mode
+--     workspace with a stale or missing URL never trips the silent-404
+--     failure mode that motivated #2339.
+--   * Push-mode is the safe default: every existing workspace continues
+--     to work exactly as before with no migration of behavior.
+--
+-- Backwards compatibility:
+--
+--   * NOT NULL with DEFAULT 'push' — the ALTER backfills existing rows.
+--   * Push-mode workspaces are unchanged: SSRF check still gates dispatch,
+--     activity logging unchanged.
+--   * Poll-mode opt-in only via POST /workspaces (delivery_mode='poll')
+--     or POST /registry/register with delivery_mode='poll'. Cannot be
+--     toggled after the fact via heartbeat — flipping mode mid-life is
+--     ambiguous (in-flight pushes vs queued polls), so an explicit
+--     PATCH /workspaces/:id/delivery_mode endpoint will be added later
+--     if the use case appears.
+--
+-- Reverse plan: the .down.sql drops the column. Any short-circuit code
+-- that reads delivery_mode would then hit a "column does not exist"
+-- error — readers fall back to push mode (behaviour pre-2339), which is
+-- the safe degradation. Acceptable for a forward-only schema; the down
+-- exists for migration tooling parity, not as a recommended runtime path.
+
+ALTER TABLE workspaces
+    ADD COLUMN IF NOT EXISTS delivery_mode TEXT NOT NULL DEFAULT 'push'
+        CHECK (delivery_mode IN ('push', 'poll'));
+
+COMMENT ON COLUMN workspaces.delivery_mode IS
+    'How inbound A2A is delivered: push (synchronous to workspaces.url) or poll (logged to activity_logs, agent reads via GET /activity?since_id=). See migration 045 + RFC #2339.';