From 2488a686a454c72a2eeadec70e82110c11751223 Mon Sep 17 00:00:00 2001
From: Jeremy McSpadden <jeremy@fluxlabs.net>
Date: Wed, 25 Mar 2026 07:45:31 -0500
Subject: [PATCH] fix(gsd): downgrade isolation mode when worktree creation
 fails

---
 src/resources/extensions/gsd/auto/session.ts  |  5 ++
 .../gsd/tests/worktree-resolver.test.ts       | 67 +++++++++++++++++++
 .../extensions/gsd/worktree-resolver.ts       | 31 +++++++++
 3 files changed, 103 insertions(+)

diff --git a/src/resources/extensions/gsd/auto/session.ts b/src/resources/extensions/gsd/auto/session.ts
index 16b94f2e1..e61298d3e 100644
--- a/src/resources/extensions/gsd/auto/session.ts
+++ b/src/resources/extensions/gsd/auto/session.ts
@@ -126,6 +126,10 @@ export class AutoSession {
   // ── Sidecar queue ─────────────────────────────────────────────────────
   sidecarQueue: SidecarItem[] = [];
 
+  // ── Isolation degradation ────────────────────────────────────────────
+  /** Set to true when worktree creation fails; prevents merge of nonexistent branch. */
+  isolationDegraded = false;
+
   // ── Dispatch circuit breakers ──────────────────────────────────────
   rewriteAttemptCount = 0;
 
@@ -217,6 +221,7 @@ export class AutoSession {
     this.pendingQuickTasks = [];
     this.sidecarQueue = [];
     this.rewriteAttemptCount = 0;
+    this.isolationDegraded = false;
 
     // Signal handler
     this.sigtermHandler = null;
diff --git a/src/resources/extensions/gsd/tests/worktree-resolver.test.ts b/src/resources/extensions/gsd/tests/worktree-resolver.test.ts
index 11718a263..c3a7f7aba 100644
--- a/src/resources/extensions/gsd/tests/worktree-resolver.test.ts
+++ b/src/resources/extensions/gsd/tests/worktree-resolver.test.ts
@@ -846,3 +846,70 @@ test("GitService is rebuilt with originalBasePath after exitMilestone", () => {
 
   assert.equal(gitServiceBasePath, "/project"); // project root, not worktree
 });
+
+// ─── Isolation Degradation Tests (#2483) ──────────────────────────────────
+
+test("enterMilestone sets isolationDegraded when worktree creation throws (#2483)", () => {
+  const s = makeSession();
+  const deps = makeDeps({
+    getAutoWorktreePath: () => null,
+    createAutoWorktree: () => {
+      throw new Error("empty repo");
+    },
+  });
+  const ctx = makeNotifyCtx();
+  const resolver = new WorktreeResolver(s, deps);
+
+  resolver.enterMilestone("M001", ctx);
+
+  assert.equal(s.isolationDegraded, true);
+  assert.equal(s.basePath, "/project"); // unchanged — error recovery
+});
+
+test("enterMilestone is no-op when isolationDegraded is true (#2483)", () => {
+  const s = makeSession();
+  s.isolationDegraded = true;
+  const deps = makeDeps();
+  const ctx = makeNotifyCtx();
+  const resolver = new WorktreeResolver(s, deps);
+
+  resolver.enterMilestone("M001", ctx);
+
+  assert.equal(s.basePath, "/project"); // unchanged
+  assert.equal(findCalls(deps.calls, "createAutoWorktree").length, 0);
+  assert.equal(findCalls(deps.calls, "enterAutoWorktree").length, 0);
+  assert.equal(findCalls(deps.calls, "shouldUseWorktreeIsolation").length, 0);
+});
+
+test("mergeAndExit is no-op when isolationDegraded is true (#2483)", () => {
+  const s = makeSession({
+    basePath: "/project",
+    originalBasePath: "/project",
+  });
+  s.isolationDegraded = true;
+  const deps = makeDeps({
+    getIsolationMode: () => "worktree",
+  });
+  const ctx = makeNotifyCtx();
+  const resolver = new WorktreeResolver(s, deps);
+
+  resolver.mergeAndExit("M001", ctx);
+
+  assert.equal(findCalls(deps.calls, "mergeMilestoneToMain").length, 0);
+  assert.equal(findCalls(deps.calls, "teardownAutoWorktree").length, 0);
+  assert.equal(findCalls(deps.calls, "getIsolationMode").length, 0);
+  assert.ok(
+    ctx.messages.some(
+      (m) => m.level === "info" && m.msg.includes("isolation was degraded"),
+    ),
+  );
+});
+
+test("isolationDegraded is reset by session.reset() (#2483)", () => {
+  const s = new AutoSession();
+  s.isolationDegraded = true;
+
+  s.reset();
+
+  assert.equal(s.isolationDegraded, false);
+});
diff --git a/src/resources/extensions/gsd/worktree-resolver.ts b/src/resources/extensions/gsd/worktree-resolver.ts
index 093899297..c245c4f95 100644
--- a/src/resources/extensions/gsd/worktree-resolver.ts
+++ b/src/resources/extensions/gsd/worktree-resolver.ts
@@ -148,6 +148,18 @@ export class WorktreeResolver {
    */
   enterMilestone(milestoneId: string, ctx: NotifyCtx): void {
     this.validateMilestoneId(milestoneId);
+
+    // If worktree creation failed earlier this session, skip all future attempts
+    if (this.s.isolationDegraded) {
+      debugLog("WorktreeResolver", {
+        action: "enterMilestone",
+        milestoneId,
+        skipped: true,
+        reason: "isolation-degraded",
+      });
+      return;
+    }
+
     if (!this.deps.shouldUseWorktreeIsolation()) {
       debugLog("WorktreeResolver", {
         action: "enterMilestone",
@@ -197,6 +209,9 @@ export class WorktreeResolver {
         `Auto-worktree creation for ${milestoneId} failed: ${msg}. Continuing in project root.`,
         "warning",
       );
+      // Degrade isolation for the rest of this session so mergeAndExit
+      // doesn't try to merge a nonexistent worktree branch (#2483)
+      this.s.isolationDegraded = true;
       // Do NOT update s.basePath — stay in project root
     }
   }
@@ -281,6 +296,22 @@ export class WorktreeResolver {
    */
   mergeAndExit(milestoneId: string, ctx: NotifyCtx): void {
     this.validateMilestoneId(milestoneId);
+
+    // If worktree creation failed earlier, skip merge — work is on current branch (#2483)
+    if (this.s.isolationDegraded) {
+      debugLog("WorktreeResolver", {
+        action: "mergeAndExit",
+        milestoneId,
+        skipped: true,
+        reason: "isolation-degraded",
+      });
+      ctx.notify(
+        `Skipping worktree merge for ${milestoneId} — isolation was degraded (worktree creation failed earlier). Work is on the current branch.`,
+        "info",
+      );
+      return;
+    }
+
     const mode = this.deps.getIsolationMode();
     debugLog("WorktreeResolver", {
       action: "mergeAndExit",