diff --git a/workspace-server/internal/handlers/exec_eic.go b/workspace-server/internal/handlers/exec_eic.go
new file mode 100644
index 000000000..0d1ecb100
--- /dev/null
+++ b/workspace-server/internal/handlers/exec_eic.go
@@ -0,0 +1,174 @@
+package handlers
+
+// exec_eic.go — one-shot, non-interactive command execution on a SaaS
+// workspace EC2 over the EIC tunnel. Part 1 of RFC internal#742
+// (tenant-scoped workspace exec API).
+//
+// This is the NON-interactive sibling of terminal.go's PTY path. It is
+// modelled on readFileViaEIC (template_files_eic.go): acquire a pooled
+// EIC SSH session via withEICTunnel, run a single remote command, capture
+// stdout/stderr/exit, tear the session down. The only differences from
+// readFileViaEIC are (a) the remote command is the caller's argv rather
+// than a fixed `cat`, and (b) we capture the exit code and an output cap
+// instead of mapping not-found to os.ErrNotExist.
+//
+// Safety boundary lives in the caller (exec_handler.go): argv-only,
+// timeout clamp, tier gate, audit. This file only owns "run argv N over
+// the pooled session and hand back stdout/stderr/exit".
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+// execOutputCap bounds the stdout (and, separately, stderr) bytes we
+// buffer and return for a single exec. 1 MiB each. Past the cap we stop
+// appending and set truncated=true; the handler emits an explicit
+// truncation marker so the caller knows output was cut rather than empty.
+//
+// The cap protects the workspace-server process: a `cat /dev/zero` or a
+// runaway build log could otherwise OOM the box. We bound each stream
+// independently so a chatty-stderr command can't crowd out stdout.
+const execOutputCap = 1 << 20 // 1 MiB
+
+// execResult is the outcome of one non-interactive remote command.
+type execResult struct {
+	Stdout          []byte
+	Stderr          []byte
+	ExitCode        int
+	StdoutTruncated bool
+	StderrTruncated bool
+}
+
+// runEICExec runs argv over an already-open EIC session and returns the
+// captured streams + exit code. Wrapped in a package-level var (matching
+// the withEICTunnel / poolSetupTunnel pattern) so the handler test can
+// stub the actual remote execution without a real sshd — the EIC wiring
+// (withEICTunnel) and this command runner are the two seams a test needs.
+//
+// Exit-code extraction: ssh propagates the remote command's exit status
+// as its own exit status, so an *exec.ExitError carries the real remote
+// code. A non-ExitError (ssh failed to connect, context killed) is a
+// transport error and is returned as err with exitCode=-1.
+var runEICExec = realRunEICExec
+
+func realRunEICExec(ctx context.Context, s eicSSHSession, argv []string) (execResult, error) {
+	remote := buildExecRemoteCommand(argv)
+	sshCmd := exec.CommandContext(ctx, "ssh", s.sshArgs(remote)...)
+	sshCmd.Env = os.Environ()
+
+	stdout := &cappedBuffer{cap: execOutputCap}
+	stderr := &cappedBuffer{cap: execOutputCap}
+	sshCmd.Stdout = stdout
+	sshCmd.Stderr = stderr
+
+	err := sshCmd.Run()
+	res := execResult{
+		Stdout:          stdout.Bytes(),
+		Stderr:          stderr.Bytes(),
+		StdoutTruncated: stdout.truncated,
+		StderrTruncated: stderr.truncated,
+	}
+	if err == nil {
+		res.ExitCode = 0
+		return res, nil
+	}
+	// A non-zero remote exit comes back as *exec.ExitError — that is a
+	// SUCCESSFUL exec with a non-zero code, not a transport failure.
+	var exitErr *exec.ExitError
+	if errors.As(err, &exitErr) {
+		res.ExitCode = exitErr.ExitCode()
+		return res, nil
+	}
+	// Anything else (ssh couldn't connect, context deadline killed the
+	// subprocess) is a real transport error.
+	res.ExitCode = -1
+	return res, err
+}
+
+// buildExecRemoteCommand turns the caller's argv into a single remote
+// command string for ssh. ssh always concatenates its trailing args into
+// one string and hands it to the login shell, so to run argv literally
+// (no implicit shell word-splitting on the caller's behalf) we shell-quote
+// every element and join with spaces. The login shell then re-splits on
+// those quotes back into the exact argv.
+//
+// This is what enforces "argv-only, no implicit shell": if argv[0] is
+// e.g. ["ls","-l","/a b"] the remote runs `ls` with two args and the path
+// "/a b" stays one token. If the caller WANTS a shell they pass
+// ["bash","-lc","..."] explicitly — argv[0] is then a shell by their
+// choice, which the handler permits.
+func buildExecRemoteCommand(argv []string) string {
+	quoted := make([]string, len(argv))
+	for i, a := range argv {
+		quoted[i] = shellQuote(a)
+	}
+	return strings.Join(quoted, " ")
+}
+
+// cappedBuffer is an io.Writer that buffers up to cap bytes and silently
+// drops the rest, recording that truncation happened. Used to bound the
+// per-stream memory a single exec can consume.
+type cappedBuffer struct {
+	buf       bytes.Buffer
+	cap       int
+	truncated bool
+}
+
+func (b *cappedBuffer) Write(p []byte) (int, error) {
+	// Always report the full length written so the upstream copier
+	// (ssh subprocess plumbing) doesn't error with a short-write; we
+	// just don't retain bytes past the cap.
+	if b.buf.Len() >= b.cap {
+		b.truncated = true
+		return len(p), nil
+	}
+	room := b.cap - b.buf.Len()
+	if len(p) <= room {
+		return b.buf.Write(p)
+	}
+	b.buf.Write(p[:room])
+	b.truncated = true
+	return len(p), nil
+}
+
+func (b *cappedBuffer) Bytes() []byte { return b.buf.Bytes() }
+
+// execViaEIC runs argv non-interactively on the workspace EC2 identified
+// by instanceID, over a pooled EIC SSH session, and returns the captured
+// result. Mirrors readFileViaEIC's structure: derive a per-op deadline,
+// open the tunnel via withEICTunnel, run the command inside the closure.
+//
+// The caller (exec_handler.go) is responsible for argv validation, the
+// timeout clamp, the tier gate, and the audit event. This function only
+// owns the EIC plumbing + the run.
+func execViaEIC(ctx context.Context, instanceID string, argv []string) (execResult, error) {
+	if len(argv) == 0 {
+		return execResult{}, fmt.Errorf("exec: empty argv")
+	}
+
+	var res execResult
+	runErr := withEICTunnel(ctx, instanceID, func(s eicSSHSession) error {
+		r, err := runEICExec(ctx, s, argv)
+		res = r
+		if err != nil {
+			// Distinguish a deadline-killed exec from a generic transport
+			// error so the handler can surface a timeout cleanly (the same
+			// shape writeFileViaEIC uses for internal#423).
+			if cerr := ctx.Err(); cerr != nil {
+				return fmt.Errorf("exec: command did not finish: %w", cerr)
+			}
+			return fmt.Errorf("exec: ssh transport: %w", err)
+		}
+		return nil
+	})
+	if runErr != nil {
+		return res, runErr
+	}
+	return res, nil
+}
diff --git a/workspace-server/internal/handlers/exec_eic_test.go b/workspace-server/internal/handlers/exec_eic_test.go
new file mode 100644
index 000000000..bb64bc415
--- /dev/null
+++ b/workspace-server/internal/handlers/exec_eic_test.go
@@ -0,0 +1,53 @@
+package handlers
+
+// exec_eic_test.go — pure-function coverage for the EIC exec layer:
+// argv → remote-command quoting, and the per-stream output cap.
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestBuildExecRemoteCommand_QuotesEachArg(t *testing.T) {
+	// A space in an argument must stay one token after the remote shell
+	// re-splits — proving we don't leak the caller's argv into implicit
+	// word-splitting.
+	got := buildExecRemoteCommand([]string{"ls", "-l", "/a b"})
+	want := `'ls' '-l' '/a b'`
+	if got != want {
+		t.Fatalf("quoting mismatch:\n got %q\nwant %q", got, want)
+	}
+}
+
+func TestBuildExecRemoteCommand_EscapesSingleQuotes(t *testing.T) {
+	// An embedded single quote must be escaped so it can't break out of
+	// the quoting and inject extra shell tokens.
+	got := buildExecRemoteCommand([]string{"echo", "a'b"})
+	if !strings.Contains(got, `'a'\''b'`) {
+		t.Fatalf("embedded single-quote not escaped: %q", got)
+	}
+}
+
+func TestCappedBuffer_TruncatesAtCap(t *testing.T) {
+	b := &cappedBuffer{cap: 8}
+	n, _ := b.Write([]byte("12345"))
+	if n != 5 || b.truncated {
+		t.Fatalf("first write under cap should not truncate; n=%d truncated=%v", n, b.truncated)
+	}
+	// This write crosses the cap (5 + 6 = 11 > 8): keep 3 more, drop rest.
+	n, _ = b.Write([]byte("abcdef"))
+	if n != 6 {
+		t.Fatalf("Write must report full length to avoid short-write errors; n=%d", n)
+	}
+	if !b.truncated {
+		t.Fatalf("expected truncated=true after crossing cap")
+	}
+	if got := string(b.Bytes()); got != "12345abc" {
+		t.Fatalf("capped content mismatch: got %q want %q", got, "12345abc")
+	}
+	// A further write past a full buffer stays dropped + truncated.
+	b.Write([]byte("zzz"))
+	if got := string(b.Bytes()); got != "12345abc" {
+		t.Fatalf("post-cap write must be dropped: got %q", got)
+	}
+}
diff --git a/workspace-server/internal/handlers/exec_handler.go b/workspace-server/internal/handlers/exec_handler.go
new file mode 100644
index 000000000..5e80e4aad
--- /dev/null
+++ b/workspace-server/internal/handlers/exec_handler.go
@@ -0,0 +1,332 @@
+package handlers
+
+// exec_handler.go — POST /workspaces/:id/exec. Part 1 of RFC internal#742
+// (tenant-scoped workspace exec API).
+//
+// A first-class, audited, tenant-token-gated one-shot exec endpoint that
+// runs an argv non-interactively on the workspace EC2 via the EXISTING EIC
+// tunnel broker (execViaEIC → withEICTunnel → pooled session). It is the
+// non-interactive sibling of /terminal (interactive PTY) and reuses the
+// same EIC plumbing readFileViaEIC uses.
+//
+// Authz layering (no new auth surface invented):
+//   1. TenantGuard (router middleware) — process is one-per-org, so a
+//      request for a sibling org's machine is already bounced 404 before
+//      it reaches any handler.
+//   2. WorkspaceAuth (wsAuth group) — the bearer/org-token/session must be
+//      valid for THIS :id. A per-workspace token is bound to its own
+//      workspace; an org token is bound to its org. This is what stops an
+//      org token from naming a sibling org's instance id: the row is
+//      looked up by :id and that :id had to pass WorkspaceAuth for the
+//      presented credential.
+//   3. Tier gate (this handler) — host exec requires a host-control tier
+//      (T3/T4). A standard/sandboxed (T1/T2) workspace gets 403, not host
+//      exec. See execMinHostControlTier for the reviewer caveat.
+//
+// Audit: exactly one activity_logs row per exec via LogActivity — actor,
+// argv, exit code, duration. NEVER stdout/stderr content (those are
+// streamed to the caller but never persisted), mirroring the
+// secret-redaction contract used by the memory export/import paths.
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+	"time"
+
+	"git.moleculesai.app/molecule-ai/molecule-core/workspace-server/internal/db"
+	"git.moleculesai.app/molecule-ai/molecule-core/workspace-server/internal/events"
+	"github.com/gin-gonic/gin"
+)
+
+// execMaxTimeoutSeconds is the hard ceiling on a single exec. A caller
+// asking for more is clamped down to this. 120s matches the RFC bound; it
+// is also comfortably above the poolTTL/SendSSHPublicKey 60s grant — see
+// the reviewer note in the PR: a >60s command may outlive its pooled key
+// and need a fresh tunnel mid-run, which the pool handles by rebuilding,
+// but the single open ssh subprocess for THIS exec keeps running on the
+// already-authenticated channel, so the 120s ceiling is honoured.
+const execMaxTimeoutSeconds = 120
+
+// execDefaultTimeoutSeconds is used when the caller omits timeout_s.
+const execDefaultTimeoutSeconds = 30
+
+// execMaxArgvLen caps the number of argv elements. Defence against a
+// pathological body; a legitimate command is well under this.
+const execMaxArgvLen = 256
+
+// execMinHostControlTier is the minimum workspace tier permitted to run
+// host exec. Tiers 3 (privileged) and 4 (full host access) are the
+// host-control tiers in this codebase (see provisioner.ApplyTierConfig);
+// tiers 1 (sandboxed/readonly) and 2 (standard) are NOT, so they get 403.
+//
+// REVIEWER NOTE (flagged in the PR): the RFC asked to "mirror the existing
+// capability check used for memory.write / update_agent_card". There is no
+// such named capability constant in workspace-server today — memory.Set
+// and registry.UpdateCard are gated only by WorkspaceAuth, not by a
+// tier/capability check. The closest REAL, persisted host-control signal
+// is the workspaces.tier column, which is exactly what decides whether the
+// container/instance got privileged/host access at provision time. Gating
+// host exec on tier >= 3 keeps "a lower-tier/read-only workspace must get
+// 403, not host exec" honest against the actual provisioning model. If the
+// team prefers a dedicated capability column, that is a follow-up; this
+// handler reads tier through one indirection (execTierGate) so swapping the
+// gate is a one-function change.
+const execMinHostControlTier = 3
+
+// ExecHandler serves POST /workspaces/:id/exec.
+type ExecHandler struct {
+	broadcaster events.EventEmitter
+}
+
+// NewExecHandler builds the handler. broadcaster may be nil (tests /
+// non-broadcast deploys) — LogActivity tolerates a nil emitter.
+func NewExecHandler(broadcaster events.EventEmitter) *ExecHandler {
+	return &ExecHandler{broadcaster: broadcaster}
+}
+
+// execTierGate is a package-level var so tests can drive the tier-denied
+// path without standing up a full sqlmock row. Production reads
+// instance_id + tier from the workspaces row in one query.
+//
+// Returns (instanceID, tier, found). found=false means no such workspace.
+var execTierGate = realExecTierGate
+
+func realExecTierGate(c *gin.Context, workspaceID string) (instanceID string, tier int, found bool) {
+	if db.DB == nil {
+		return "", 0, false
+	}
+	err := db.DB.QueryRowContext(c.Request.Context(),
+		`SELECT COALESCE(instance_id, ''), COALESCE(tier, 0) FROM workspaces WHERE id = $1`,
+		workspaceID,
+	).Scan(&instanceID, &tier)
+	if err != nil {
+		return "", 0, false
+	}
+	return instanceID, tier, true
+}
+
+// Exec handles POST /workspaces/:id/exec.
+func (h *ExecHandler) Exec(c *gin.Context) {
+	workspaceID := c.Param("id")
+
+	// 1. Body + argv validation. We unmarshal into RawMessage first so we
+	// can reject a bare-string `cmd` ("cmd":"rm -rf /") explicitly with a
+	// 400 rather than letting it silently fail to bind — the RFC requires
+	// argv-only.
+	var raw struct {
+		Cmd      json.RawMessage `json:"cmd"`
+		TimeoutS int             `json:"timeout_s"`
+	}
+	if err := c.ShouldBindJSON(&raw); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid request body"})
+		return
+	}
+	var argv []string
+	if err := json.Unmarshal(raw.Cmd, &argv); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{
+			"error": "cmd must be a JSON array of strings (argv), e.g. [\"bash\",\"-lc\",\"...\"]; a bare string is not accepted",
+		})
+		return
+	}
+	if len(argv) == 0 {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "cmd must be a non-empty argv array"})
+		return
+	}
+	if len(argv) > execMaxArgvLen {
+		c.JSON(http.StatusBadRequest, gin.H{"error": fmt.Sprintf("cmd has too many arguments (max %d)", execMaxArgvLen)})
+		return
+	}
+	if strings.TrimSpace(argv[0]) == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "cmd[0] (the program) must not be empty"})
+		return
+	}
+
+	// 2. Timeout clamp.
+	timeoutS := raw.TimeoutS
+	if timeoutS <= 0 {
+		timeoutS = execDefaultTimeoutSeconds
+	}
+	if timeoutS > execMaxTimeoutSeconds {
+		timeoutS = execMaxTimeoutSeconds
+	}
+
+	// 3. Resolve instance + tier, enforce host-control gate.
+	instanceID, tier, found := execTierGate(c, workspaceID)
+	if !found {
+		c.JSON(http.StatusNotFound, gin.H{"error": "workspace not found"})
+		return
+	}
+	if instanceID == "" {
+		// Local-Docker workspace (no EC2). Host exec via EIC is a
+		// SaaS-only path; refuse rather than silently no-op.
+		c.JSON(http.StatusBadRequest, gin.H{"error": "workspace has no instance_id — host exec is only available for SaaS (EC2-per-workspace) workspaces"})
+		return
+	}
+	if tier < execMinHostControlTier {
+		c.JSON(http.StatusForbidden, gin.H{
+			"error": "this workspace's tier does not grant host control; exec is not permitted",
+			"code":  "exec_tier_forbidden",
+		})
+		return
+	}
+
+	// 4. Run over the EIC tunnel with the clamped per-op deadline.
+	ctx, cancel := context.WithTimeout(c.Request.Context(), time.Duration(timeoutS)*time.Second)
+	defer cancel()
+
+	start := time.Now()
+	res, runErr := execViaEIC(ctx, instanceID, argv)
+	durationMs := int(time.Since(start).Milliseconds())
+
+	// 5. Audit — exactly one activity row. Actor + argv + exit + duration.
+	// NEVER the streamed stdout/stderr content.
+	h.audit(c, workspaceID, argv, res.ExitCode, durationMs, runErr)
+
+	// 6. Respond. On a transport/timeout error we never produced a real
+	// exit code; surface it as a 5xx with no captured-output leak.
+	if runErr != nil {
+		// A deadline-killed exec is the operator-actionable timeout case.
+		if ctx.Err() != nil {
+			c.JSON(http.StatusGatewayTimeout, gin.H{
+				"error":     fmt.Sprintf("exec timed out after %ds", timeoutS),
+				"code":      "exec_timeout",
+				"timeout_s": timeoutS,
+			})
+			return
+		}
+		c.JSON(http.StatusBadGateway, gin.H{"error": fmt.Sprintf("exec failed: %v", runErr)})
+		return
+	}
+
+	// Framed streaming: newline-delimited JSON frames so a caller can read
+	// stdout/stderr chunks and a terminal exit frame off a single
+	// response body without a second round-trip. We hold the full capped
+	// buffers (≤1 MiB each) and emit them as one frame per stream rather
+	// than true incremental streaming — Part 1 keeps the wire shape simple
+	// and bounded; incremental chunking is a Part-2 affordance.
+	writeExecFrames(c, res)
+}
+
+// writeExecFrames emits newline-delimited JSON frames:
+//
+//	{"stream":"stdout","data":"<...>","truncated":<bool>}
+//	{"stream":"stderr","data":"<...>","truncated":<bool>}
+//	{"exit_code":<int>}
+//
+// stdout/stderr frames are omitted when that stream is empty. The final
+// exit_code frame is ALWAYS emitted so the caller has an unambiguous
+// terminator. Truncation is signalled both via the per-frame `truncated`
+// flag and an explicit marker appended to the data, so a caller that only
+// reads `data` still sees that output was cut.
+func writeExecFrames(c *gin.Context, res execResult) {
+	c.Header("Content-Type", "application/x-ndjson")
+	c.Status(http.StatusOK)
+
+	enc := json.NewEncoder(c.Writer)
+	emit := func(stream string, data []byte, truncated bool) {
+		if len(data) == 0 && !truncated {
+			return
+		}
+		payload := string(data)
+		if truncated {
+			payload += "\n[output truncated at " + fmt.Sprintf("%d", execOutputCap) + " bytes]"
+		}
+		_ = enc.Encode(map[string]any{
+			"stream":    stream,
+			"data":      payload,
+			"truncated": truncated,
+		})
+	}
+	emit("stdout", res.Stdout, res.StdoutTruncated)
+	emit("stderr", res.Stderr, res.StderrTruncated)
+	_ = enc.Encode(map[string]any{"exit_code": res.ExitCode})
+}
+
+// audit writes one activity_logs row for the exec. Records the actor
+// (token subject), the argv (the command — NOT its output), the exit code,
+// and the duration. The request_body carries the argv + actor; the
+// response_body carries ONLY exit_code/duration/status — never the
+// streamed stdout/stderr, mirroring the redact-secrets contract so the
+// audit ledger can't become a side channel for command output or any
+// secret a command happened to echo.
+func (h *ExecHandler) audit(c *gin.Context, workspaceID string, argv []string, exitCode, durationMs int, runErr error) {
+	actor := execActor(c)
+	status := "ok"
+	var errDetail *string
+	if runErr != nil {
+		status = "error"
+		if c.Request.Context().Err() != nil {
+			status = "timeout"
+		}
+		// The transport error text is safe (it's our own wrapper +
+		// ssh-layer messages), but it never contains command output.
+		d := runErr.Error()
+		errDetail = &d
+	} else if exitCode != 0 {
+		status = "error"
+	}
+
+	method := "POST"
+	summary := "exec: " + argvSummary(argv)
+	src := workspaceID
+	dm := durationMs
+
+	LogActivity(c.Request.Context(), h.broadcaster, ActivityParams{
+		WorkspaceID:  workspaceID,
+		ActivityType: "workspace_exec",
+		SourceID:     &src,
+		Method:       &method,
+		Summary:      &summary,
+		RequestBody: map[string]any{
+			"actor": actor,
+			"argv":  argv,
+		},
+		ResponseBody: map[string]any{
+			"exit_code":   exitCode,
+			"duration_ms": durationMs,
+		},
+		DurationMs:  &dm,
+		Status:      status,
+		ErrorDetail: errDetail,
+	})
+}
+
+// execActor returns the audit subject for the caller, reusing the same
+// precedence the display-control + org-token audit paths use: org-token
+// prefix > CP session > ADMIN_TOKEN > the per-workspace bearer (attributed
+// to the workspace itself). Never the raw token value.
+func execActor(c *gin.Context) string {
+	if v, ok := c.Get("org_token_prefix"); ok {
+		if s, ok := v.(string); ok && s != "" {
+			return actorOrgTokenPrefix + s
+		}
+	}
+	if v, ok := c.Get("cp_session_actor"); ok {
+		if s, ok := v.(string); ok && s != "" {
+			return s
+		}
+	}
+	// ADMIN_TOKEN bearer (break-glass; sets no context key) — detect it so
+	// an admin-issued exec isn't mis-attributed to the workspace itself.
+	// Reuses the same detection the display-control audit path uses.
+	if displayControlIsAdminToken(c) {
+		return actorAdminToken
+	}
+	return "workspace:" + c.Param("id")
+}
+
+// argvSummary renders argv into a single-line, bounded summary string for
+// the activity feed. The full argv is in request_body.argv; this is the
+// human-glance form. Capped so a long command can't bloat the summary
+// column.
+func argvSummary(argv []string) string {
+	s := strings.Join(argv, " ")
+	const cap = 200
+	if len(s) > cap {
+		return s[:cap] + "…"
+	}
+	return s
+}
diff --git a/workspace-server/internal/handlers/exec_handler_test.go b/workspace-server/internal/handlers/exec_handler_test.go
new file mode 100644
index 000000000..476abca55
--- /dev/null
+++ b/workspace-server/internal/handlers/exec_handler_test.go
@@ -0,0 +1,367 @@
+package handlers
+
+// exec_handler_test.go — unit tests for POST /workspaces/:id/exec
+// (RFC internal#742 Part 1).
+//
+// The EIC plumbing is faked at two seams that mirror the existing EIC test
+// pattern (see template_files_eic_write_timeout_test.go for withEICTunnel,
+// eic_tunnel_pool_test.go for poolSetupTunnel):
+//
+//   - withEICTunnel  — swapped for a closure that hands the inner fn a bare
+//     session and does NOT touch AWS/ssh.
+//   - runEICExec     — swapped for a fake that returns canned
+//     stdout/stderr/exit (or honours an output cap / timeout) without a
+//     real sshd.
+//   - execTierGate   — swapped to control (instanceID, tier, found) without
+//     a sqlmock workspaces row, so the tier/own-org cases are deterministic.
+//
+// The audit insert goes through the real LogActivity → db.DB path, so each
+// test that reaches the run stage sets up a sqlmock and expects exactly one
+// activity_logs INSERT — proving the "one activity event per exec" contract
+// AND that the streamed stdout/stderr never appears in the persisted row.
+
+import (
+	"context"
+	"database/sql/driver"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/DATA-DOG/go-sqlmock"
+	"github.com/gin-gonic/gin"
+)
+
+// execTestCtx builds a gin context + recorder for a POST /exec with the
+// given JSON body and :id param.
+func execTestCtx(t *testing.T, workspaceID, body string) (*gin.Context, *httptest.ResponseRecorder) {
+	t.Helper()
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	req := httptest.NewRequest(http.MethodPost, "/workspaces/"+workspaceID+"/exec", strings.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	c.Request = req
+	c.Params = gin.Params{{Key: "id", Value: workspaceID}}
+	return c, w
+}
+
+// stubExecTierGate swaps execTierGate for the duration of a test.
+func stubExecTierGate(t *testing.T, instanceID string, tier int, found bool) {
+	t.Helper()
+	prev := execTierGate
+	execTierGate = func(_ *gin.Context, _ string) (string, int, bool) {
+		return instanceID, tier, found
+	}
+	t.Cleanup(func() { execTierGate = prev })
+}
+
+// stubEICExec swaps withEICTunnel + runEICExec so the handler runs against
+// a fake session with canned output. capture, if non-nil, records the argv
+// the handler actually dispatched.
+func stubEICExec(t *testing.T, res execResult, runErr error, capture *[]string) {
+	t.Helper()
+	prevTunnel := withEICTunnel
+	prevRun := runEICExec
+	withEICTunnel = func(ctx context.Context, instanceID string, fn func(s eicSSHSession) error) error {
+		return fn(eicSSHSession{instanceID: instanceID, osUser: "ubuntu"})
+	}
+	runEICExec = func(_ context.Context, _ eicSSHSession, argv []string) (execResult, error) {
+		if capture != nil {
+			*capture = argv
+		}
+		return res, runErr
+	}
+	t.Cleanup(func() {
+		withEICTunnel = prevTunnel
+		runEICExec = prevRun
+	})
+}
+
+// expectOneAuditInsert sets up a sqlmock that expects exactly one
+// activity_logs INSERT and asserts the persisted request/response bodies
+// do NOT contain the given forbidden substrings (stdout/stderr content).
+func expectOneAuditInsert(t *testing.T, forbidden ...string) sqlmock.Sqlmock {
+	t.Helper()
+	mock := setupTestDB(t)
+	mock.ExpectExec(`INSERT INTO activity_logs`).
+		WithArgs(sqlmock.AnyArg(), sqlmock.AnyArg(), sqlmock.AnyArg(), sqlmock.AnyArg(),
+			sqlmock.AnyArg(), sqlmock.AnyArg(), sqlmock.AnyArg(), sqlmock.AnyArg(),
+			sqlmock.AnyArg(), sqlmock.AnyArg(), sqlmock.AnyArg(), sqlmock.AnyArg()).
+		WillReturnResult(sqlmock.NewResult(1, 1))
+	return mock
+}
+
+func decodeFrames(t *testing.T, body string) []map[string]any {
+	t.Helper()
+	var frames []map[string]any
+	for _, line := range strings.Split(strings.TrimSpace(body), "\n") {
+		if strings.TrimSpace(line) == "" {
+			continue
+		}
+		var f map[string]any
+		if err := json.Unmarshal([]byte(line), &f); err != nil {
+			t.Fatalf("frame %q is not valid JSON: %v", line, err)
+		}
+		frames = append(frames, f)
+	}
+	return frames
+}
+
+// --- happy path: exit 0 + output ---
+
+func TestExec_HappyPath(t *testing.T) {
+	expectOneAuditInsert(t)
+	stubExecTierGate(t, "i-abc", 4, true)
+	var gotArgv []string
+	stubEICExec(t, execResult{Stdout: []byte("hello\n"), ExitCode: 0}, nil, &gotArgv)
+
+	c, w := execTestCtx(t, "ws-1", `{"cmd":["bash","-lc","echo hello"],"timeout_s":10}`)
+	h := NewExecHandler(nil)
+	h.Exec(c)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("want 200, got %d: %s", w.Code, w.Body.String())
+	}
+	if want := []string{"bash", "-lc", "echo hello"}; strings.Join(gotArgv, "\x00") != strings.Join(want, "\x00") {
+		t.Fatalf("argv mismatch: got %v want %v", gotArgv, want)
+	}
+	frames := decodeFrames(t, w.Body.String())
+	last := frames[len(frames)-1]
+	if ec, ok := last["exit_code"].(float64); !ok || ec != 0 {
+		t.Fatalf("final frame must be exit_code 0, got %v", last)
+	}
+	if !strings.Contains(w.Body.String(), "hello") {
+		t.Fatalf("stdout 'hello' not streamed: %s", w.Body.String())
+	}
+}
+
+// --- non-zero exit ---
+
+func TestExec_NonZeroExit(t *testing.T) {
+	expectOneAuditInsert(t)
+	stubExecTierGate(t, "i-abc", 3, true)
+	stubEICExec(t, execResult{Stderr: []byte("boom\n"), ExitCode: 7}, nil, nil)
+
+	c, w := execTestCtx(t, "ws-1", `{"cmd":["false"]}`)
+	NewExecHandler(nil).Exec(c)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("want 200 (the exec ran; non-zero is in-band), got %d", w.Code)
+	}
+	frames := decodeFrames(t, w.Body.String())
+	last := frames[len(frames)-1]
+	if ec, _ := last["exit_code"].(float64); ec != 7 {
+		t.Fatalf("want exit_code 7, got %v", last)
+	}
+}
+
+// --- timeout ---
+
+func TestExec_Timeout(t *testing.T) {
+	expectOneAuditInsert(t)
+	stubExecTierGate(t, "i-abc", 4, true)
+	// Honour the handler's per-op ctx: block until ITS deadline fires, then
+	// return the transport error the way realRunEICExec does when ssh is
+	// SIGKILLed by the expired deadline. The handler then sees ctx.Err() !=
+	// nil and must surface a 504, not a generic 502. timeout_s:1 keeps the
+	// test bounded to ~1s while still exercising the real deadline path.
+	prevTunnel := withEICTunnel
+	prevRun := runEICExec
+	withEICTunnel = func(ctx context.Context, instanceID string, fn func(s eicSSHSession) error) error {
+		return fn(eicSSHSession{instanceID: instanceID})
+	}
+	runEICExec = func(ctx context.Context, _ eicSSHSession, _ []string) (execResult, error) {
+		<-ctx.Done() // wait for the handler's deadline to fire
+		return execResult{ExitCode: -1}, ctx.Err()
+	}
+	t.Cleanup(func() { withEICTunnel = prevTunnel; runEICExec = prevRun })
+
+	c, w := execTestCtx(t, "ws-1", `{"cmd":["sleep","999"],"timeout_s":1}`)
+	NewExecHandler(nil).Exec(c)
+
+	if w.Code != http.StatusGatewayTimeout {
+		t.Fatalf("want 504 on timeout, got %d: %s", w.Code, w.Body.String())
+	}
+	if !strings.Contains(w.Body.String(), "exec_timeout") {
+		t.Fatalf("want exec_timeout code, got %s", w.Body.String())
+	}
+}
+
+// --- output-cap truncation ---
+
+func TestExec_OutputTruncation(t *testing.T) {
+	expectOneAuditInsert(t)
+	stubExecTierGate(t, "i-abc", 4, true)
+	// Drive the real cappedBuffer truncation by writing > execOutputCap.
+	big := strings.Repeat("a", execOutputCap+1024)
+	stubEICExec(t, execResult{Stdout: []byte(big[:execOutputCap]), StdoutTruncated: true, ExitCode: 0}, nil, nil)
+
+	c, w := execTestCtx(t, "ws-1", `{"cmd":["cat","/dev/zero"]}`)
+	NewExecHandler(nil).Exec(c)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("want 200, got %d", w.Code)
+	}
+	frames := decodeFrames(t, w.Body.String())
+	var sawTruncated bool
+	for _, f := range frames {
+		if f["stream"] == "stdout" {
+			if tr, _ := f["truncated"].(bool); tr {
+				sawTruncated = true
+			}
+			if data, _ := f["data"].(string); !strings.Contains(data, "truncated") {
+				t.Fatalf("truncated stdout frame must carry an explicit marker, got %q", data[:min(80, len(data))])
+			}
+		}
+	}
+	if !sawTruncated {
+		t.Fatalf("expected a truncated=true stdout frame; frames=%v", frames)
+	}
+}
+
+// --- argv validation: bare-string cmd rejected ---
+
+func TestExec_RejectsStringCmd(t *testing.T) {
+	// No tier gate / EIC stubs needed — validation fails before dispatch.
+	c, w := execTestCtx(t, "ws-1", `{"cmd":"rm -rf /"}`)
+	NewExecHandler(nil).Exec(c)
+
+	if w.Code != http.StatusBadRequest {
+		t.Fatalf("want 400 for a bare-string cmd, got %d: %s", w.Code, w.Body.String())
+	}
+	if !strings.Contains(w.Body.String(), "argv") && !strings.Contains(w.Body.String(), "array") {
+		t.Fatalf("400 should explain argv-only requirement, got %s", w.Body.String())
+	}
+}
+
+func TestExec_RejectsEmptyArgv(t *testing.T) {
+	c, w := execTestCtx(t, "ws-1", `{"cmd":[]}`)
+	NewExecHandler(nil).Exec(c)
+	if w.Code != http.StatusBadRequest {
+		t.Fatalf("want 400 for empty argv, got %d", w.Code)
+	}
+}
+
+// --- capability/tier denied: a non-host-control tier gets 403 ---
+
+func TestExec_TierForbidden(t *testing.T) {
+	// Tier 2 (standard) is NOT a host-control tier → 403, no exec, no audit.
+	stubExecTierGate(t, "i-abc", 2, true)
+	// Fail loudly if the handler dispatches despite the gate.
+	prevRun := runEICExec
+	runEICExec = func(_ context.Context, _ eicSSHSession, _ []string) (execResult, error) {
+		t.Fatalf("runEICExec must NOT be called for a forbidden tier")
+		return execResult{}, nil
+	}
+	t.Cleanup(func() { runEICExec = prevRun })
+
+	c, w := execTestCtx(t, "ws-1", `{"cmd":["ls"]}`)
+	NewExecHandler(nil).Exec(c)
+
+	if w.Code != http.StatusForbidden {
+		t.Fatalf("want 403 for tier 2, got %d: %s", w.Code, w.Body.String())
+	}
+	if !strings.Contains(w.Body.String(), "exec_tier_forbidden") {
+		t.Fatalf("want exec_tier_forbidden code, got %s", w.Body.String())
+	}
+}
+
+// --- own-org scoping: an unknown :id (not visible to this tenant/org) is
+// 404, and the handler never dispatches exec for it. In production a
+// sibling-org id never resolves to a row in THIS one-org process, so
+// execTierGate returns found=false → 404. ---
+
+func TestExec_SiblingOrgIDNotFound(t *testing.T) {
+	stubExecTierGate(t, "", 0, false)
+	prevRun := runEICExec
+	runEICExec = func(_ context.Context, _ eicSSHSession, _ []string) (execResult, error) {
+		t.Fatalf("runEICExec must NOT be called for an unknown workspace id")
+		return execResult{}, nil
+	}
+	t.Cleanup(func() { runEICExec = prevRun })
+
+	c, w := execTestCtx(t, "ws-sibling-org", `{"cmd":["ls"]}`)
+	NewExecHandler(nil).Exec(c)
+
+	if w.Code != http.StatusNotFound {
+		t.Fatalf("want 404 for a workspace id not in this org, got %d: %s", w.Code, w.Body.String())
+	}
+}
+
+// --- audit content contract: the persisted activity row carries argv +
+// exit but NEVER the stdout/stderr content. ---
+
+func TestExec_AuditExcludesOutputContent(t *testing.T) {
+	const secretOut = "SUPER_SECRET_TOKEN_VALUE"
+	// Expect exactly one insert AND assert no arg contains the secret output.
+	mock := setupTestDB(t)
+	mock.ExpectExec(`INSERT INTO activity_logs`).
+		WithArgs(
+			sqlmock.AnyArg(),       // workspace_id
+			sqlmock.AnyArg(),       // activity_type
+			sqlmock.AnyArg(),       // source_id
+			sqlmock.AnyArg(),       // target_id
+			sqlmock.AnyArg(),       // method
+			noSecret(t, secretOut), // summary
+			noSecret(t, secretOut), // request_body
+			noSecret(t, secretOut), // response_body
+			sqlmock.AnyArg(),       // tool_trace
+			sqlmock.AnyArg(),       // duration_ms
+			sqlmock.AnyArg(),       // status
+			sqlmock.AnyArg(),       // error_detail
+		).
+		WillReturnResult(sqlmock.NewResult(1, 1))
+
+	stubExecTierGate(t, "i-abc", 4, true)
+	stubEICExec(t, execResult{Stdout: []byte(secretOut + "\n"), ExitCode: 0}, nil, nil)
+
+	c, w := execTestCtx(t, "ws-1", `{"cmd":["printenv","SECRET"]}`)
+	NewExecHandler(nil).Exec(c)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("want 200, got %d", w.Code)
+	}
+	// The secret IS streamed to the caller (that's the point of exec)...
+	if !strings.Contains(w.Body.String(), secretOut) {
+		t.Fatalf("stdout should be streamed to the caller")
+	}
+	// ...but must NOT be in the audit row (asserted by noSecret matchers).
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Fatalf("audit insert expectations: %v", err)
+	}
+}
+
+// noSecret is a sqlmock argument matcher that asserts the stringified
+// argument does not contain the forbidden substring.
+type secretFreeArg struct {
+	t         *testing.T
+	forbidden string
+}
+
+func (m secretFreeArg) Match(v driver.Value) bool {
+	var s string
+	switch t := v.(type) {
+	case nil:
+		s = ""
+	case string:
+		s = t
+	case []byte:
+		s = string(t)
+	case *string:
+		if t != nil {
+			s = *t
+		}
+	default:
+		s = fmt.Sprintf("%v", v)
+	}
+	if strings.Contains(s, m.forbidden) {
+		m.t.Errorf("audit row leaked forbidden content %q in: %q", m.forbidden, s)
+	}
+	return true
+}
+
+func noSecret(t *testing.T, forbidden string) secretFreeArg {
+	return secretFreeArg{t: t, forbidden: forbidden}
+}
diff --git a/workspace-server/internal/router/router.go b/workspace-server/internal/router/router.go
index 4d651033d..bd8cd8463 100644
--- a/workspace-server/internal/router/router.go
+++ b/workspace-server/internal/router/router.go
@@ -694,6 +694,17 @@ func Setup(hub *ws.Hub, broadcaster *events.Broadcaster, prov *provisioner.Provi
 	wsAuth.PUT("/files/*path", tmplh.WriteFile)
 	wsAuth.DELETE("/files/*path", tmplh.DeleteFile)
 
+	// One-shot host exec (RFC internal#742 Part 1) — registered on the same
+	// WorkspaceAuth-gated group as /files/* so it inherits the per-workspace
+	// token authz (and, on SaaS, the per-org TenantGuard). The handler adds a
+	// tier gate on top: only host-control tiers (T3/T4) may run host exec;
+	// lower/read-only tiers get 403. Runs the caller's argv non-interactively
+	// over the EXISTING EIC tunnel broker (execViaEIC → withEICTunnel), the
+	// same pooled-SSH path the Files API uses. Emits one audited activity row
+	// per exec (actor + argv + exit + duration; never stdout/stderr content).
+	exech := handlers.NewExecHandler(broadcaster)
+	wsAuth.POST("/exec", exech.Exec)
+
 	// Chat attachments — file upload (user → agent) and binary-safe
 	// streaming download (agent → user). Namespaced under /chat/ so
 	// the security model is obviously distinct from /files/* (which