feat(workspaces): delivery_mode column + poll-mode register flow (#2339 PR 1)

Adds workspaces.delivery_mode (push, default | poll) and lets the register
handler accept poll-mode workspaces with no URL. This is the foundation
for the unified poll/push delivery design in #2339 — Telegram-getUpdates
shape for external runtimes that have no public URL.

What this PR does:

  - Migration 045: NOT NULL TEXT column, default 'push', CHECK constraint
    on the two valid values.
  - models.Workspace + RegisterPayload + CreateWorkspacePayload gain a
    DeliveryMode field. RegisterPayload.URL drops the `binding:"required"`
    tag — the handler now enforces it conditionally on the resolved mode.
  - Register handler: validates explicit delivery_mode if set; resolves
    effective mode (payload value, else stored row value, else push) AFTER
    the C18 token check; validates URL only when effective mode is push;
    persists delivery_mode in the upsert; returns it in the response;
    skips URL caching when payload.URL is empty.
  - CreateWorkspace handler: persists delivery_mode (defaults to push) in
    the same INSERT, validates it before any side effects.

What this PR does NOT do (intentional, follow-up PRs):

  - PR 2: short-circuit ProxyA2A for poll-mode workspaces (skip SSRF +
    dispatch, log a2a_receive activity, return 200).
  - PR 3: since_id cursor on GET /activity for lossless polling.
  - Plugin v0.2 in molecule-mcp-claude-channel: cursor persistence + a
    register helper that creates poll-mode workspaces.

Backwards compatibility: every existing workspace stays push-mode (schema
default) with identical behavior. New tests:
TestRegister_PollMode_AcceptsEmptyURL,
TestRegister_PushMode_RejectsEmptyURL,
TestRegister_InvalidDeliveryMode,
TestRegister_PollMode_PreservesExistingValue. All existing register +
create tests updated to expect the new delivery_mode column in the
INSERT args.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

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)

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 {

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)
+	}
+}

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)

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()

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").

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"`

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;

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.';