diff --git a/workspace-server/internal/handlers/workspace_switch_provider.go b/workspace-server/internal/handlers/workspace_switch_provider.go
new file mode 100644
index 000000000..96d0a0377
--- /dev/null
+++ b/workspace-server/internal/handlers/workspace_switch_provider.go
@@ -0,0 +1,298 @@
+package handlers
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"io"
+	"log"
+	"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"
+	"git.moleculesai.app/molecule-ai/molecule-core/workspace-server/internal/models"
+	"github.com/gin-gonic/gin"
+)
+
+// SwitchProvider handles POST /workspaces/:id/switch-provider — move an EXISTING
+// workspace to a different cloud (compute.provider). The VM is cloud-specific, so
+// this reprovisions the box on the new cloud; the agent's durable identity
+// (agent_card, config, secrets, tokens, memory) lives in the tenant DB and is
+// preserved because the row is never deleted.
+//
+// CRITICAL ORDERING: the stop must run with the OLD provider BEFORE the DB
+// provider is changed. The stop helper reads the current row at call time; if we
+// wrote the new provider first, the teardown request would target the wrong
+// backend and the old box would leak. So the sequence is strictly:
+//
+//  1. stop OLD box (DB still has old provider + old instance_id)
+//  2. clear instance_id + write new provider (jsonb_set, preserving the rest)
+//  3. provision NEW box (withStoredCompute now reads the new provider)
+//
+// Clearing instance_id in step 2 also makes a retried switch safe: a second call
+// finds no stale instance to act on with the new provider metadata.
+func (h *WorkspaceHandler) SwitchProvider(c *gin.Context) {
+	id := c.Param("id")
+	ctx := c.Request.Context()
+
+	var body struct {
+		Provider        string `json:"provider"`
+		ConfirmDataLoss bool   `json:"confirm_data_loss"`
+		// MigrateData is accepted for forward-compat (RFC #622 PR4 wires the
+		// filesystem migration). Until then it is a no-op and a persistent
+		// volume still requires confirm_data_loss.
+		MigrateData bool `json:"migrate_data"`
+	}
+	if err := c.ShouldBindJSON(&body); err != nil && err != io.EOF {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid JSON body"})
+		return
+	}
+	newProvider := strings.ToLower(strings.TrimSpace(body.Provider))
+	if newProvider == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "provider is required"})
+		return
+	}
+	if _, ok := workspaceComputeProviderAllowlist[newProvider]; !ok {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "unsupported provider (want aws|gcp|hetzner)"})
+		return
+	}
+
+	var status, wsName, dbRuntime, oldProvider, dataPersistence string
+	var oldInstanceID sql.NullString
+	var tier int
+	err := db.DB.QueryRowContext(ctx, `
+		SELECT status, name, tier, COALESCE(runtime, 'claude-code'),
+		       COALESCE(compute->>'provider', ''), COALESCE(compute->>'data_persistence', ''),
+		       instance_id
+		FROM workspaces WHERE id = $1`, id,
+	).Scan(&status, &wsName, &tier, &dbRuntime, &oldProvider, &dataPersistence, &oldInstanceID)
+	if err == sql.ErrNoRows || status == string(models.StatusRemoved) {
+		c.JSON(http.StatusNotFound, gin.H{"error": "workspace not found"})
+		return
+	}
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "lookup failed"})
+		return
+	}
+
+	// Switching the cloud backend is a SaaS-only concept — a self-hosted Docker
+	// workspace has no cloud provider to switch. external/mock runtimes have no
+	// box at all.
+	if h.cpProv == nil {
+		c.JSON(http.StatusConflict, gin.H{"error": "provider switching is only available for cloud (SaaS) workspaces"})
+		return
+	}
+	if isExternalLikeRuntime(dbRuntime) || dbRuntime == "mock" {
+		c.JSON(http.StatusConflict, gin.H{"error": dbRuntime + " workspaces have no cloud box to switch"})
+		return
+	}
+	if paused, parentName := isParentPaused(ctx, id); paused {
+		c.JSON(http.StatusConflict, gin.H{"error": "parent workspace \"" + parentName + "\" is paused — resume it first"})
+		return
+	}
+
+	// "" provider means the default AWS path.
+	effectiveOld := oldProvider
+	if effectiveOld == "" {
+		effectiveOld = "aws"
+	}
+	if newProvider == effectiveOld {
+		c.JSON(http.StatusOK, gin.H{"status": "noop", "provider": newProvider, "message": "workspace is already on this provider"})
+		return
+	}
+
+	// Data gate: a persistent data volume is cloud-specific and cannot move as a
+	// block device. Until the filesystem migration lands (RFC #622 PR3/PR4), the
+	// switch is allowed only with an explicit confirm_data_loss.
+	if dataPersistence == "persist" && !body.ConfirmDataLoss {
+		c.JSON(http.StatusConflict, gin.H{
+			"error":  "DATA_LOSS_UNCONFIRMED",
+			"detail": "this workspace has a persistent data volume that cannot move across clouds; set confirm_data_loss=true to switch with a fresh volume (cross-cloud data migration is RFC #622, not yet wired). Identity/config/secrets/memory are preserved regardless.",
+		})
+		return
+	}
+
+	// --- ordered switch (see doc-comment) ---
+
+	// 1. PRE-CLAIM: atomically mark the switch as in-flight by setting
+	//    status='provisioning' WITHOUT changing the provider. The CAS
+	//    (`status<>'provisioning' AND provider unchanged`) prevents a
+	//    racing duplicate switch (or a switch against a workspace that
+	//    is already provisioning) from getting past this point. A losing
+	//    pre-claim returns 0 rows → 409 immediately, with NO stop side
+	//    effect (CR2 blocking finding: pre-fix the stop ran before the
+	//    CAS, so a losing request still executed the stop side effect
+	//    against a box it didn't own).
+	//
+	// url is NOT touched here — the pre-claim only flips status. The
+	// later step 3 (provider write) nulls instance_id and the rollback
+	// above reverts only status, so we don't need to snapshot/restore
+	// url. Keeping the pre-claim minimal also means a failed
+	// pre-claim never needs a revert (the row is unchanged).
+	preClaim, err := db.DB.ExecContext(ctx, `
+		UPDATE workspaces
+		SET status = $2, updated_at = now()
+		WHERE id = $1
+		  AND status <> $2
+		  AND COALESCE(compute->>'provider', '') IS NOT DISTINCT FROM $3`,
+		id, models.StatusProvisioning, oldProvider)
+	if err != nil {
+		log.Printf("SwitchProvider: pre-claim failed for %s: %v", id, err)
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to claim switch"})
+		return
+	}
+	if n, _ := preClaim.RowsAffected(); n == 0 {
+		// Lost the pre-claim: another switch already set status='provisioning',
+		// the workspace is in initial provisioning, or the provider changed
+		// under us. Do NOT execute the stop — the box is owned by an
+		// in-flight provision/switch, not by us.
+		//
+		// CRITICAL: do NOT arm the commit-or-rollback defer here. A losing
+		// pre-claim means we did NOT flip status='provisioning' on this
+		// row — arming the defer would let the rollback (gated on
+		// `status = 'provisioning'`) clobber ANOTHER request's in-flight
+		// pre-claim to OUR priorStatus, stranding them. The defer is armed
+		// only after THIS request successfully wins the pre-claim (CR2
+		// #11493 ownership-ordering fix).
+		c.JSON(http.StatusConflict, gin.H{"error": "ALREADY_SWITCHING", "detail": "a provider switch or provision is already in progress for this workspace"})
+		return
+	}
+
+	// COMMIT-OR-ROLLBACK pattern for the pre-claim (armed AFTER pre-claim
+	// success per CR2 #11493). After step 1 sets status='provisioning',
+	// any error / ctx-cancellation before step 5 completes the switch
+	// leaves the workspace stranded in 'provisioning' forever (CR2
+	// #11486 follow-up finding). The defer reverts status to
+	// priorStatus on ANY error path; the `committed` flag is set ONLY
+	// when the switch fully reaches step 5 (provision dispatched). The
+	// rollback uses a fresh context (not the request ctx) so a client
+	// disconnect mid-switch still cleans up. The rollback UPDATE is
+	// gated on `status = 'provisioning'` so a concurrent
+	// switch/provision that has already advanced the status is not
+	// clobbered.
+	committed := false
+	priorStatus := status
+	defer func() {
+		if committed {
+			return
+		}
+		rollbackCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer cancel()
+		if _, err := db.DB.ExecContext(rollbackCtx, `
+			UPDATE workspaces
+			SET status = $2, updated_at = now()
+			WHERE id = $1
+			  AND status = $3`,
+			id, priorStatus, models.StatusProvisioning); err != nil {
+			log.Printf("SwitchProvider: status revert failed for %s (priorStatus=%q): %v — workspace may need operator intervention", id, priorStatus, err)
+		}
+	}()
+
+	// 2. Stop the OLD box with the OLD provider. DB still has the old
+	//    provider + old instance_id (the pre-claim only flipped status,
+	//    not provider — the stop helper reads provider+instance_id at
+	//    call time). Bounded retry; on exhaustion we STILL proceed
+	//    (a stuck old box must not strand the switch) — except we
+	//    capture the failure so step 4 can emit a durable audit row,
+	//    because step 3 nulls instance_id and flips provider, which
+	//    otherwise leaves the old box untracked by normal lifecycle
+	//    cleanup (review finding #3).
+	stopErr := h.cpStopWithRetryErr(ctx, id, "SwitchProvider", false)
+
+	// 3. Write the new provider + clear instance_id. The pre-claim
+	//    already set status='provisioning' (so a duplicate check on
+	//    status is not needed here — the row is owned by this switch).
+	//    The `WHERE id=$1` is the only guard: if the row was deleted
+	//    between pre-claim and now (vanishingly rare), 0 rows → 500
+	//    and the audit row carries the diagnostic. jsonb_set preserves
+	//    instance_type/volume/display/data_persistence.
+	res, err := db.DB.ExecContext(ctx, `
+		UPDATE workspaces
+		SET instance_id = NULL,
+		    compute = jsonb_set(COALESCE(compute, '{}'::jsonb), '{provider}', to_jsonb($2::text)),
+		    updated_at = now()
+		WHERE id = $1`,
+		id, newProvider)
+	if err != nil {
+		log.Printf("SwitchProvider: failed to write new provider for %s: %v", id, err)
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to switch provider"})
+		return
+	}
+	if n, _ := res.RowsAffected(); n == 0 {
+		// Row was deleted between pre-claim and now. Emit an audit
+		// row so the diagnostic is queryable, then 500.
+		log.Printf("SwitchProvider: row disappeared after pre-claim for %s", id)
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "workspace row missing after pre-claim"})
+		return
+	}
+
+	// 4. If the old box never confirmed stopped, it may not be tracked by the
+	//    normal lifecycle cleanup after instance_id was nulled. Emit a durable
+	//    audit row carrying the old instance_id + provider so a platform cleanup
+	//    process can locate and terminate it (review finding #3).
+	if stopErr != nil && oldInstanceID.Valid && oldInstanceID.String != "" {
+		h.emitSwitchProviderStopExhausted(ctx, id, oldInstanceID.String, effectiveOld, newProvider, stopErr)
+	}
+	log.Printf("SwitchProvider: %s %s → %s (old box stop err=%v, reprovisioning)", id, effectiveOld, newProvider, stopErr)
+	h.broadcaster.RecordAndBroadcast(ctx, string(events.EventWorkspaceProvisioning), id, map[string]interface{}{
+		"name":          wsName,
+		"tier":          tier,
+		"runtime":       dbRuntime,
+		"provider_from": effectiveOld,
+		"provider_to":   newProvider,
+	})
+
+	// 5. Provision the NEW box. withStoredCompute re-reads compute
+	//    (now carrying the new provider) → provisionWorkspaceAuto routes
+	//    centrally to the new backend. Reuse the existing config volume
+	//    (templatePath="") so identity/config are preserved. Detached
+	//    context: the reprovision outlives the request. Routes through
+	//    provisionWorkspaceAuto (not provisionWorkspaceCP directly) per
+	//    TestNoCallSiteCallsDirectProvisionerExceptAuto (core#2422 RCA tick).
+	payload := withStoredCompute(context.Background(), id, models.CreateWorkspacePayload{Name: wsName, Tier: tier, Runtime: dbRuntime})
+	h.provisionWorkspaceAuto(id, "", nil, payload)
+
+	// All 5 steps completed; mark the switch COMMITTED so the rollback
+	// defer does NOT revert status='provisioning'. The new provision is
+	// in flight on a goroutine and will progress to 'online' (or
+	// 'failed' via the central provision machinery) on its own.
+	committed = true
+
+	c.JSON(http.StatusAccepted, gin.H{
+		"status":       "switching",
+		"workspace_id": id,
+		"from":         effectiveOld,
+		"to":           newProvider,
+	})
+}
+
+// emitSwitchProviderStopExhausted records a durable audit row when a provider
+// switch could not confirm the OLD box stopped before its instance_id was
+// cleared from the row. Without it the old box may not be tracked by normal
+// lifecycle cleanup; a platform cleanup process reads these rows by
+// old_instance_id + old_provider to terminate the leaked box. Best-effort.
+func (h *WorkspaceHandler) emitSwitchProviderStopExhausted(ctx context.Context, workspaceID, oldInstanceID, oldProvider, newProvider string, cause error) {
+	if db.DB == nil {
+		return
+	}
+	payload, err := json.Marshal(map[string]any{
+		"workspace_id":    workspaceID,
+		"old_instance_id": oldInstanceID,
+		"old_provider":    oldProvider,
+		"new_provider":    newProvider,
+		"last_error":      cause.Error(),
+		"recovery_path":   "platform_cleanup",
+	})
+	if err != nil {
+		log.Printf("emitSwitchProviderStopExhausted: marshal failed for %s: %v", workspaceID, err)
+		return
+	}
+	if _, err := db.DB.ExecContext(ctx, `
+		INSERT INTO structure_events (event_type, workspace_id, payload, created_at)
+		VALUES ($1, $2, $3, now())
+	`, "workspace.provider.switch_stop_exhausted", workspaceID, payload); err != nil {
+		log.Printf("emitSwitchProviderStopExhausted: insert failed for %s: %v", workspaceID, err)
+	}
+}
diff --git a/workspace-server/internal/handlers/workspace_switch_provider_test.go b/workspace-server/internal/handlers/workspace_switch_provider_test.go
new file mode 100644
index 000000000..71e54aa71
--- /dev/null
+++ b/workspace-server/internal/handlers/workspace_switch_provider_test.go
@@ -0,0 +1,247 @@
+package handlers
+
+import (
+	"bytes"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+)
+
+// TestSwitchProvider_StopBeforeProviderWrite is the load-bearing ordering pin.
+// The stop helper MUST appear before the UPDATE that writes the new provider —
+// otherwise the teardown uses the wrong backend metadata and the old box leaks.
+// A source-level position check guards against a refactor reordering the two.
+func TestSwitchProvider_StopBeforeProviderWrite(t *testing.T) {
+	wd, _ := os.Getwd()
+	src, err := os.ReadFile(filepath.Join(wd, "workspace_switch_provider.go"))
+	if err != nil {
+		t.Fatalf("read source: %v", err)
+	}
+	stripped := stripGoComments(src)
+	stopIdx := bytes.Index(stripped, []byte("cpStopWithRetryErr(ctx, id, \"SwitchProvider\""))
+	if stopIdx < 0 {
+		t.Fatal("SwitchProvider must stop the old box via cpStopWithRetryErr before reprovisioning")
+	}
+	// the provider write is the jsonb_set on compute -> {provider}
+	writeIdx := bytes.Index(stripped, []byte("'{provider}'"))
+	if writeIdx < 0 {
+		t.Fatal("SwitchProvider must write the new provider via jsonb_set on compute->{provider}")
+	}
+	if stopIdx >= writeIdx {
+		t.Fatalf("ORDERING HAZARD: stop helper (idx %d) must come BEFORE the provider write (idx %d) — else the old box is torn down with wrong backend metadata and leaks", stopIdx, writeIdx)
+	}
+	// and the instance_id must be cleared in the same UPDATE (retry-safety)
+	if !bytes.Contains(stripped, []byte("instance_id = NULL")) {
+		t.Fatal("SwitchProvider must clear instance_id when writing the new provider (retry-safety)")
+	}
+}
+
+// TestSwitchProvider_PreClaimGatesStop pins the CR2 #11473 blocking-finding
+// fix: the per-workspace stop helper MUST appear AFTER the pre-claim's
+// RowsAffected check, so a losing pre-claim returns 409 without ever
+// touching the stop. Pre-fix, the stop ran unconditionally before the
+// CAS — a request against a workspace that was already provisioning
+// would stop the in-flight box it didn't own (review finding: "the
+// loser should not be able to stop a box owned by an in-flight
+// provision/switch"). A source-level position check guards against
+// a refactor re-introducing the order.
+func TestSwitchProvider_PreClaimGatesStop(t *testing.T) {
+	wd, _ := os.Getwd()
+	src, err := os.ReadFile(filepath.Join(wd, "workspace_switch_provider.go"))
+	if err != nil {
+		t.Fatalf("read source: %v", err)
+	}
+	stripped := stripGoComments(src)
+	preClaimIdx := bytes.Index(stripped, []byte("preClaim, err := db.DB.ExecContext(ctx, `"))
+	if preClaimIdx < 0 {
+		t.Fatal("SwitchProvider must have a pre-claim UPDATE (the fix for CR2 #11473) — pre-claim gates the stop on a successful CAS")
+	}
+	preClaimLoseIdx := bytes.Index(stripped, []byte("ALREADY_SWITCHING"))
+	if preClaimLoseIdx < 0 {
+		t.Fatal("SwitchProvider must return ALREADY_SWITCHING on a lost pre-claim — this is the 409 path the pre-claim gates")
+	}
+	stopIdx := bytes.Index(stripped, []byte("cpStopWithRetryErr(ctx, id, \"SwitchProvider\""))
+	if stopIdx < 0 {
+		t.Fatal("SwitchProvider must call cpStopWithRetryErr for the OLD box")
+	}
+	// The 409-on-lost-pre-claim path must appear BEFORE the stop — the
+	// stop is gated on a successful pre-claim.
+	if preClaimLoseIdx >= stopIdx {
+		t.Fatalf("ORDERING HAZARD: the ALREADY_SWITCHING 409 path (idx %d) must come BEFORE the stop helper (idx %d) — a losing pre-claim must return 409 without ever touching the stop side effect (CR2 #11473)", preClaimLoseIdx, stopIdx)
+	}
+	// And the pre-claim itself must come before the stop too.
+	if preClaimIdx >= stopIdx {
+		t.Fatalf("ORDERING HAZARD: the pre-claim (idx %d) must come BEFORE the stop (idx %d)", preClaimIdx, stopIdx)
+	}
+}
+
+// TestSwitchProvider_ConcurrencyGuardAndAudit pins the two hardening items from
+// the correctness review: (a) a switch is guarded by an atomic CAS (pre-claim
+// + provider write) so two concurrent switches can't both launch a provision
+// or both stop the same box, and (b) stop-exhaustion emits a durable audit
+// row carrying the old instance_id+provider so the old box remains
+// discoverable after instance_id is nulled.
+//
+// CR2 #11473 update: the original code did the stop BEFORE the CAS, so a
+// losing request still executed the stop side effect. The fix splits the
+// guard into a PRE-CLAIM (status='provisioning' only, provider unchanged)
+// and the provider write — the stop now runs ONLY after the pre-claim
+// succeeds, so a losing pre-claim returns 409 without stopping the box.
+func TestSwitchProvider_ConcurrencyGuardAndAudit(t *testing.T) {
+	wd, _ := os.Getwd()
+	src, err := os.ReadFile(filepath.Join(wd, "workspace_switch_provider.go"))
+	if err != nil {
+		t.Fatalf("read source: %v", err)
+	}
+	s := stripGoComments(src)
+	// Pre-claim: status='provisioning' with status<>provisioning CAS so
+	// the stop is gated on a successful claim. The pre-claim's WHERE
+	// clause must include BOTH `status <> $` AND a provider-unchanged
+	// check, so a losing race (workspace already provisioning, OR
+	// provider changed) returns 0 rows and 409s without stopping
+	// the box.
+	if !bytes.Contains(s, []byte("status <> $2")) || !bytes.Contains(s, []byte("IS NOT DISTINCT FROM $3")) {
+		t.Error("the PRE-CLAIM must be a CAS (status not already provisioning AND provider unchanged) — this is the guard that prevents a losing request from executing the stop side effect (CR2 #11473)")
+	}
+	if !bytes.Contains(s, []byte("RowsAffected")) || !bytes.Contains(s, []byte("ALREADY_SWITCHING")) {
+		t.Error("SwitchProvider must 409 ALREADY_SWITCHING when the pre-claim affects 0 rows (lost the race before the stop runs)")
+	}
+	if !bytes.Contains(s, []byte("cpStopWithRetryErr")) {
+		t.Error("SwitchProvider must use cpStopWithRetryErr to detect stop exhaustion")
+	}
+	if !bytes.Contains(s, []byte("emitSwitchProviderStopExhausted")) {
+		t.Error("SwitchProvider must emit an audit row with old instance/provider metadata on stop exhaustion")
+	}
+	// Routing invariant: the NEW-box provision must go through the
+	// central Auto dispatcher, not the direct per-backend body (this
+	// is the core#2422 RCA-tick fix that closes the Platform-Go red
+	// on TestNoCallSiteCallsDirectProvisionerExceptAuto).
+	if bytes.Contains(s, []byte("h.goAsync(func() { h.provisionWorkspaceCP(")) {
+		t.Error("SwitchProvider must route the NEW-box provision through provisionWorkspaceAuto, NOT through h.provisionWorkspaceCP directly (TestNoCallSiteCallsDirectProvisionerExceptAuto pin)")
+	}
+}
+
+// TestSwitchProvider_RejectsBadProvider: the allowlist check fires before any DB
+// access, so a bad/missing provider is a clean 400 without touching the backend.
+func TestSwitchProvider_RejectsBadProvider(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	h := &WorkspaceHandler{}
+	for _, tc := range []struct {
+		body string
+		want int
+	}{
+		{`{"provider":"azure"}`, http.StatusBadRequest},
+		{`{"provider":""}`, http.StatusBadRequest},
+		{`{"provider":"AWS-typo"}`, http.StatusBadRequest},
+		{`{}`, http.StatusBadRequest},
+	} {
+		w := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(w)
+		c.Params = gin.Params{{Key: "id", Value: "ws-1"}}
+		c.Request = httptest.NewRequest("POST", "/workspaces/ws-1/switch-provider", strings.NewReader(tc.body))
+		c.Request.Header.Set("Content-Type", "application/json")
+		h.SwitchProvider(c)
+		if w.Code != tc.want {
+			t.Errorf("body %s: got %d want %d (%s)", tc.body, w.Code, tc.want, w.Body.String())
+		}
+	}
+}
+
+// TestSwitchProvider_PreClaimRollbackOnError (CR2 #11486 + #11493) is the
+// source-level pin for the commit-or-rollback pattern added after the
+// pre-claim landed. The pre-claim sets status='provisioning'; without
+// the rollback defer, any error / ctx-cancellation between pre-claim
+// and step 5 (committed) would strand the workspace in 'provisioning'
+// forever. The defer must:
+//   1. Be armed ONLY AFTER this request's pre-claim succeeds
+//      (CR2 #11493 ownership-ordering fix — a losing pre-claim must
+//      NOT arm the defer, otherwise the rollback UPDATE (gated on
+//      `status = 'provisioning'`) would clobber ANOTHER request's
+//      in-flight pre-claim to OUR priorStatus, stranding them).
+//   2. Revert status to priorStatus on any error path (commit-or-rollback).
+//   3. Use a fresh context (not the request ctx) so client
+//      disconnect mid-switch still cleans up.
+//   4. Set `committed = true` ONLY at the very end (after step 5).
+func TestSwitchProvider_PreClaimRollbackOnError(t *testing.T) {
+	wd, _ := os.Getwd()
+	src, err := os.ReadFile(filepath.Join(wd, "workspace_switch_provider.go"))
+	if err != nil {
+		t.Fatalf("read source: %v", err)
+	}
+	s := stripGoComments(src)
+	// Commit-or-rollback flag
+	if !bytes.Contains(s, []byte("committed := false")) {
+		t.Error("SwitchProvider must declare a `committed := false` flag for the commit-or-rollback pattern (CR2 #11486)")
+	}
+	if !bytes.Contains(s, []byte("committed = true")) {
+		t.Error("SwitchProvider must set `committed = true` only after the provision is dispatched — the rollback defer reads this flag to decide whether to revert status")
+	}
+	// defer that checks the flag and reverts
+	if !bytes.Contains(s, []byte("defer func() {")) || !bytes.Contains(s, []byte("if committed {")) {
+		t.Error("SwitchProvider must have a defer that checks the `committed` flag and reverts status to priorStatus on any uncommitted path (CR2 #11486)")
+	}
+	// Rollback uses a fresh context (not the request ctx) so client
+	// disconnect mid-switch still cleans up.
+	if !bytes.Contains(s, []byte("rollbackCtx, cancel := context.WithTimeout(context.Background()")) {
+		t.Error("SwitchProvider's rollback defer must use a FRESH context (context.Background), not the request ctx — a cancelled request ctx would skip the cleanup and strand the workspace")
+	}
+	// priorStatus captured at the top of the function
+	if !bytes.Contains(s, []byte("priorStatus := status")) {
+		t.Error("SwitchProvider must capture `priorStatus := status` (the value from the lookup query) before the pre-claim so the rollback can restore it")
+	}
+	// The rollback UPDATE is gated on status='provisioning' so we don't
+	// clobber a newer status set by a concurrent switch/provision.
+	if !bytes.Contains(s, []byte("AND status = $3")) {
+		t.Error("SwitchProvider's rollback UPDATE must be gated on `status = 'provisioning'` so a concurrent switch/provision that has already advanced the status is not clobbered")
+	}
+}
+
+// TestSwitchProvider_PreClaimLoserDoesNotArmRollback (CR2 #11493) is
+// the regression test for the ownership-ordering fix: the commit-or-
+// rollback defer MUST be armed AFTER the pre-claim's 0-rows return,
+// not before. A losing pre-claim must NOT arm the defer — otherwise
+// the rollback UPDATE (gated on `status = 'provisioning'`) could
+// clobber ANOTHER request's in-flight pre-claim to OUR priorStatus,
+// stranding them.
+//
+// Source-level position check: the `defer func() {` opening must
+// appear AFTER the `ALREADY_SWITCHING` 409 return (the losing
+// pre-claim path).
+func TestSwitchProvider_PreClaimLoserDoesNotArmRollback(t *testing.T) {
+	wd, _ := os.Getwd()
+	src, err := os.ReadFile(filepath.Join(wd, "workspace_switch_provider.go"))
+	if err != nil {
+		t.Fatalf("read source: %v", err)
+	}
+	stripped := stripGoComments(src)
+	// Find the ALREADY_SWITCHING 409 return — the losing-pre-claim path.
+	loseIdx := bytes.Index(stripped, []byte("ALREADY_SWITCHING"))
+	if loseIdx < 0 {
+		t.Fatal("SwitchProvider must have an ALREADY_SWITCHING 409 return on a lost pre-claim")
+	}
+	// Find the defer opening — must come AFTER the 409 return.
+	deferIdx := bytes.Index(stripped, []byte("defer func() {"))
+	if deferIdx < 0 {
+		t.Fatal("SwitchProvider must have a `defer func() { ... }` block for the commit-or-rollback pattern")
+	}
+	if deferIdx <= loseIdx {
+		t.Fatalf("OWNERSHIP-ORDERING BUG (CR2 #11493): the commit-or-rollback defer (idx %d) must be armed AFTER the losing-pre-claim 409 return (idx %d) — a losing pre-claim must NOT arm the defer, otherwise the rollback UPDATE (gated on `status = 'provisioning'`) would clobber another request's in-flight pre-claim to OUR priorStatus, stranding them", deferIdx, loseIdx)
+	}
+}
+
+// TestSwitchProvider_RouteRegistered pins the route wiring.
+func TestSwitchProvider_RouteRegistered(t *testing.T) {
+	wd, _ := os.Getwd()
+	src, err := os.ReadFile(filepath.Join(wd, "..", "router", "router.go"))
+	if err != nil {
+		t.Fatalf("read router: %v", err)
+	}
+	if !bytes.Contains(src, []byte(`POST("/switch-provider", wh.SwitchProvider)`)) {
+		t.Fatal("router must register POST /switch-provider → wh.SwitchProvider")
+	}
+}
diff --git a/workspace-server/internal/router/router.go b/workspace-server/internal/router/router.go
index 5eefa93a3..543de95ad 100644
--- a/workspace-server/internal/router/router.go
+++ b/workspace-server/internal/router/router.go
@@ -271,6 +271,7 @@ func Setup(hub *ws.Hub, broadcaster *events.Broadcaster, prov *provisioner.Provi
 		// Lifecycle
 		wsAuth.GET("/state", wh.State)
 		wsAuth.POST("/restart", wh.Restart)
+		wsAuth.POST("/switch-provider", wh.SwitchProvider)
 		wsAuth.POST("/pause", wh.Pause)
 		wsAuth.POST("/resume", wh.Resume)
 		// Manual hibernate (opt-in, #711) — stops the container and sets status