diff --git a/packages/adapters/claude-local/src/server/execute.remote.test.ts b/packages/adapters/claude-local/src/server/execute.remote.test.ts
index 58118a838e6..3a80ff225ff 100644
--- a/packages/adapters/claude-local/src/server/execute.remote.test.ts
+++ b/packages/adapters/claude-local/src/server/execute.remote.test.ts
@@ -1,4 +1,4 @@
-import { mkdir, mkdtemp, rm, writeFile } from "node:fs/promises";
+import { mkdir, mkdtemp, rm, stat, writeFile } from "node:fs/promises";
 import os from "node:os";
 import path from "node:path";
 import { afterEach, describe, expect, it, vi } from "vitest";
@@ -95,7 +95,7 @@ describe("claude remote execution", () => {
     }
   });
 
-  it("prepares the workspace, syncs Claude runtime assets, and restores workspace changes for remote SSH execution", async () => {
+  it.each([true, false])("prepares and restores a copied SSH workspace (already exists: %s)", async (exists) => {
     vi.stubEnv("CLAUDE_CODE_USE_BEDROCK", "1");
     vi.stubEnv("ANTHROPIC_MODEL", "host-only-model");
     const rootDir = await mkdtemp(path.join(os.tmpdir(), "paperclip-claude-remote-"));
@@ -104,7 +104,11 @@ describe("claude remote execution", () => {
     const alternateWorkspaceDir = path.join(rootDir, "workspace-other");
     const instructionsPath = path.join(rootDir, "instructions.md");
     const managedRemoteWorkspace = "/remote/workspace/.paperclip-runtime/runs/run-1/workspace";
-    await mkdir(workspaceDir, { recursive: true });
+    if (exists) await mkdir(workspaceDir, { recursive: true });
+    prepareWorkspaceForSshExecution.mockImplementationOnce(async () => {
+      expect((await stat(workspaceDir)).isDirectory()).toBe(true);
+      return { gitBacked: false };
+    });
     await mkdir(alternateWorkspaceDir, { recursive: true });
     await writeFile(instructionsPath, "Use the remote workspace.\n", "utf8");
 
diff --git a/packages/adapters/claude-local/src/server/execute.ts b/packages/adapters/claude-local/src/server/execute.ts
index 40a7318b094..68c94789b5a 100644
--- a/packages/adapters/claude-local/src/server/execute.ts
+++ b/packages/adapters/claude-local/src/server/execute.ts
@@ -219,7 +219,7 @@ async function buildClaudeRuntimeConfig(input: ClaudeExecutionInput): Promise<Cl
     executionTargetIsRemote,
     executionCwd: effectiveExecutionCwd,
   });
-  if (!executionTargetIsRemote) {
+  if (executionTarget?.workspaceRealization?.mode !== "in_place") {
     await ensureAbsoluteDirectory(cwd, { createIfMissing: true });
   }
 
diff --git a/packages/paperclip-runner/src/drivers/acpx/installation-integrity.test.ts b/packages/paperclip-runner/src/drivers/acpx/installation-integrity.test.ts
index b3f17569448..e562d591568 100644
--- a/packages/paperclip-runner/src/drivers/acpx/installation-integrity.test.ts
+++ b/packages/paperclip-runner/src/drivers/acpx/installation-integrity.test.ts
@@ -64,7 +64,7 @@ afterEach(async () => {
 describe("ACPX installation integrity", () => {
   describe.each(["runtime", "command"] as const)("%s executable hydration", (kind) => {
   const verify = kind === "runtime" ? openVerifiedRuntimeExecutable : inspectCommand;
-  it.each(["once", "every_read", "wrong_digest", "mode", "mtime", "replacement", "symlink", "second_content"] as const)("requires stable full re-verification after a ctime-only transition (%s)", async (transition) => {
+  it.each(["once", "every_read", "wrong_digest", "mode", "mtime", "replacement", "symlink", "second_content", "uid", "gid", "nlink"] as const)("requires stable full re-verification after a ctime-only transition (%s)", async (transition) => {
     const directory = await mkdtemp(join(tmpdir(), "paperclip-runtime-hydration-"));
     temporaryDirectories.push(directory);
     const executable = join(directory, "runtime");
@@ -74,8 +74,15 @@ describe("ACPX installation integrity", () => {
     const probe = await open(executable, "r");
     const prototype = Object.getPrototypeOf(probe) as FileHandle;
     const originalRead = probe.read;
+    const originalStat = probe.stat;
     await probe.close();
     let reads = 0;
+    // Model ownership changes without requiring privileged chown in the test.
+    const statSpy = vi.spyOn(prototype, "stat").mockImplementation(async function (this: FileHandle, ...args: Parameters<FileHandle["stat"]>) {
+      const metadata = await Reflect.apply(originalStat, this, args);
+      if (reads > 0 && (transition === "uid" || transition === "gid")) metadata[transition] += 1n;
+      return metadata;
+    });
     const readSpy = vi.spyOn(prototype, "read").mockImplementation(async function (this: FileHandle, ...args: Parameters<FileHandle["read"]>) {
       if (reads === 1 && transition === "second_content") {
         await writeFile(executable, Buffer.alloc(bytes.length, 120));
@@ -93,6 +100,7 @@ describe("ACPX installation integrity", () => {
         const after = await stat(executable, { bigint: true });
         expect(after.ctimeNs).not.toBe(before.ctimeNs);
         expect([after.dev, after.ino, after.size, after.mode, after.mtimeNs]).toEqual([before.dev, before.ino, before.size, before.mode, before.mtimeNs]);
+        if (transition === "nlink") await link(executable, `${executable}.link`);
         if (transition === "mode") await chmod(executable, 0o700);
         if (transition === "mtime") await utimes(executable, new Date(0), new Date(0));
         if (transition === "replacement" || transition === "symlink") {
@@ -117,7 +125,7 @@ describe("ACPX installation integrity", () => {
         await expect(verify(executable, digest, "fixture")).rejects.toThrow(transition === "wrong_digest" ? "digest mismatch" : "changed while it was verified");
       }
       expect(reads).toBe(["once", "every_read", "second_content"].includes(transition) ? 2 : 1);
-    } finally { readSpy.mockRestore(); }
+    } finally { readSpy.mockRestore(); statSpy.mockRestore(); }
   });
 
   });
diff --git a/packages/paperclip-runner/src/drivers/acpx/installation-integrity.ts b/packages/paperclip-runner/src/drivers/acpx/installation-integrity.ts
index b51da6efe5b..b1a3a2f2285 100644
--- a/packages/paperclip-runner/src/drivers/acpx/installation-integrity.ts
+++ b/packages/paperclip-runner/src/drivers/acpx/installation-integrity.ts
@@ -1188,7 +1188,10 @@ async function openVerifiedExecutable(
       const beforeIdentity = fileIdentity(before);
       if (
         !sameIdentity(fileIdentity(lexicalBaseline), beforeIdentity) ||
-        lexicalBaseline.mode !== before.mode
+        lexicalBaseline.mode !== before.mode ||
+        lexicalBaseline.uid !== before.uid ||
+        lexicalBaseline.gid !== before.gid ||
+        lexicalBaseline.nlink !== before.nlink
       ) {
         throw new Error(
           `${label} changed while it was verified`,
@@ -1226,7 +1229,13 @@ async function openVerifiedExecutable(
         !lexicalAfter.isFile() ||
         !sameIdentity(fileIdentity(lexicalAfter), afterIdentity) ||
         lexicalAfter.mode !== after.mode ||
+        lexicalAfter.uid !== after.uid ||
+        lexicalAfter.gid !== after.gid ||
+        lexicalAfter.nlink !== after.nlink ||
         before.mode !== after.mode ||
+        before.uid !== after.uid ||
+        before.gid !== after.gid ||
+        before.nlink !== after.nlink ||
         !sameIdentity(
           { ...beforeIdentity, changedNanoseconds: afterIdentity.changedNanoseconds },
           afterIdentity,
diff --git a/packages/paperclip-runner/src/drivers/codex/codex-security-config.ts b/packages/paperclip-runner/src/drivers/codex/codex-security-config.ts
index d02e0cfb4b0..aa16e4ace3d 100644
--- a/packages/paperclip-runner/src/drivers/codex/codex-security-config.ts
+++ b/packages/paperclip-runner/src/drivers/codex/codex-security-config.ts
@@ -250,6 +250,8 @@ export function createIsolatedCodexAppServerArgs(
   readOnlyRoots: string[] = [],
   /** Server-registered run copy, never an environment/config-supplied root. */
   instructionWorkingCopyRoot?: string,
+  /** Separate controller-registered personal directory, never an ambient env grant. */
+  persistentAgentHome?: string,
 ): string[] {
   const explicitSource = source;
   source ??= process.env;
@@ -268,7 +270,9 @@ export function createIsolatedCodexAppServerArgs(
   const commandEnvironment = codexCommandEnvironment(source);
   // Selected task values are inherited, never serialized into configuration argv.
   for (const key of configuredEnvironmentKeys(explicitSource)) delete commandEnvironment[key];
-  if (instructionWorkingCopyRoot && source.AGENT_HOME === instructionWorkingCopyRoot) commandEnvironment.AGENT_HOME = instructionWorkingCopyRoot;
+  const registeredAgentHome = persistentAgentHome ?? instructionWorkingCopyRoot;
+  if (registeredAgentHome && source.AGENT_HOME === registeredAgentHome) commandEnvironment.AGENT_HOME = registeredAgentHome;
+  const registeredWritableRoots = [...new Set([instructionWorkingCopyRoot, persistentAgentHome].filter((root): root is string => Boolean(root)))];
   const shellEnvironmentKeys = [...new Set([...inheritedGitHubKeys, ...Object.keys(commandEnvironment)])].sort();
   if (source.PAPERCLIP_GITHUB_LAUNCHER_DIR) readOnlyRoots = [...readOnlyRoots, source.PAPERCLIP_GITHUB_LAUNCHER_DIR];
   const deniedHostRoots = [
@@ -289,7 +293,7 @@ export function createIsolatedCodexAppServerArgs(
     ...readOnlyRoots.map((path) => `${tomlString(resolve(path))}="read"`),
     ...gitRoots.read.map((path) => `${tomlString(path)}="read"`),
     ...gitRoots.write.map((path) => `${tomlString(path)}="write"`),
-    ...(instructionWorkingCopyRoot ? [`${tomlString(resolve(instructionWorkingCopyRoot))}="write"`] : []),
+    ...registeredWritableRoots.map((root) => `${tomlString(resolve(root))}="write"`),
     ...(source.PAPERCLIP_GITHUB_BROKER_TOKEN && source.GH_CONFIG_DIR
       ? [`${tomlString(resolve(source.GH_CONFIG_DIR))}="write"`] : []),
     `":workspace_roots"={"."="write"}`,
@@ -301,7 +305,7 @@ export function createIsolatedCodexAppServerArgs(
     ...deniedHostRoots.map((path) => `${tomlString(path)}="none"`),
     ...readOnlyRoots.map((path) => `${tomlString(resolve(path))}="read"`),
     ...[...gitRoots.read, ...gitRoots.write].map((path) => `${tomlString(path)}="read"`),
-    ...(instructionWorkingCopyRoot ? [`${tomlString(resolve(instructionWorkingCopyRoot))}="read"`] : []),
+    ...registeredWritableRoots.map((root) => `${tomlString(resolve(root))}="read"`),
     ...(source.PAPERCLIP_GITHUB_BROKER_TOKEN && source.GH_CONFIG_DIR
       ? [`${tomlString(resolve(source.GH_CONFIG_DIR))}="write"`] : []),
     `":workspace_roots"={"."="read"}`,
diff --git a/packages/paperclip-runner/src/drivers/runtime-context-materializer.test.ts b/packages/paperclip-runner/src/drivers/runtime-context-materializer.test.ts
index 4e68be2944b..79fcd583bff 100644
--- a/packages/paperclip-runner/src/drivers/runtime-context-materializer.test.ts
+++ b/packages/paperclip-runner/src/drivers/runtime-context-materializer.test.ts
@@ -527,3 +527,16 @@ it("exposes a trusted persistent personal directory without instruction files",
   expect(supplied).not.toContain('AGENT_HOME="/untrusted"');
   expect(createRunnerdCodexAppServerArgs(options).join("\n")).not.toContain("AGENT_HOME");
 });
+
+it("grants separate registered personal and instruction directories to Codex shells", () => {
+  const args = createRunnerdCodexAppServerArgs({
+    environment: { AGENT_HOME: "/untrusted" }, codexHome: "/private-provider",
+    persistentAgentHome: "/personal/agent", instructionWorkingCopyRoot: "/instructions/run",
+  }).join("\n");
+  expect(args).toContain('AGENT_HOME="/personal/agent"');
+  for (const root of ["/personal/agent", "/instructions/run"]) {
+    expect(args).toContain(`"${root}"="write"`);
+    expect(args).toContain(`"${root}"="read"`);
+  }
+  expect(args).not.toContain("/untrusted");
+});
diff --git a/packages/paperclip-runner/src/live/runnerd-codex-transport.ts b/packages/paperclip-runner/src/live/runnerd-codex-transport.ts
index c127a1955db..a9a82213524 100644
--- a/packages/paperclip-runner/src/live/runnerd-codex-transport.ts
+++ b/packages/paperclip-runner/src/live/runnerd-codex-transport.ts
@@ -3493,7 +3493,8 @@ export function createRunnerdCodexAppServerArgs(input: {
       ...(input.persistentAgentHome ? { AGENT_HOME: input.persistentAgentHome } : {}),
     },
     [...(input.readOnlyRoots ?? []), ...codexExecutableReadOnlyRoots(input.environment ?? {}, input.codexCommand)],
-    input.instructionWorkingCopyRoot ?? input.persistentAgentHome,
+    input.instructionWorkingCopyRoot,
+    input.persistentAgentHome,
   );
 }
 
diff --git a/packages/shared/src/types/workspace-runtime.ts b/packages/shared/src/types/workspace-runtime.ts
index 25a8dbf6549..479260c30c3 100644
--- a/packages/shared/src/types/workspace-runtime.ts
+++ b/packages/shared/src/types/workspace-runtime.ts
@@ -351,6 +351,8 @@ export interface WorkspaceRealizationRequest {
     repoRef: string | null;
     strategy: "project_primary" | "git_worktree";
     branchName: string | null;
+    /** Attach this exact pre-existing branch without creating or resetting it. */
+    existingBranch?: string;
     worktreePath: string | null;
   };
   /**
diff --git a/server/src/__tests__/adapter-registry.test.ts b/server/src/__tests__/adapter-registry.test.ts
index 05ff46ada71..43c4ede5acf 100644
--- a/server/src/__tests__/adapter-registry.test.ts
+++ b/server/src/__tests__/adapter-registry.test.ts
@@ -332,7 +332,7 @@ describe("server adapter registry", () => {
     expect(config).not.toHaveProperty("engine");
   });
 
-  it("verifies the Claude harness on a computer after checking its platform", async () => {
+  it.each([true, false])("retains the unverified ACPX warning after a computer Claude CLI probe (succeeds: %s)", async (succeeds) => {
     const calls: string[] = [];
     const result = await requireServerAdapter("paperclip_runner").testEnvironment({
       companyId: "company-1", adapterType: "paperclip_runner",
@@ -342,13 +342,15 @@ describe("server adapter registry", () => {
           calls.push(input.command);
           const stdout = input.command === "claude" ? JSON.stringify({ type: "result", result: "hello", usage: { input_tokens: 1, output_tokens: 1 } })
             : input.args?.some(arg => arg.includes("uname -s")) ? "Linux\nx86_64\n" : "";
-          return { exitCode: 0, timedOut: false, stdout, stderr: "", signal: null, pid: null, startedAt: new Date().toISOString() };
+          return { exitCode: input.command === "claude" && !succeeds ? 1 : 0, timedOut: false, stdout, stderr: "", signal: null, pid: null, startedAt: new Date().toISOString() };
         } },
       } as never,
     });
     expect(calls).toContain("claude");
-    expect(result.checks).toContainEqual(expect.objectContaining({ code: "claude_hello_probe_passed", level: "info" }));
-    expect(result.checks.some(check => check.level === "error")).toBe(false);
+    expect(result.status).toBe(succeeds ? "warn" : "fail");
+    expect(result.checks).toContainEqual(expect.objectContaining({ code: "acpx_remote_runtime_unverified", level: "warn" }));
+    if (succeeds) expect(result.checks).toContainEqual(expect.objectContaining({ code: "claude_hello_probe_passed", level: "info" }));
+    expect(result.checks.some(check => check.level === "error")).toBe(!succeeds);
   });
 
   it.each([true, false])("checks actual local ACPX installation readiness (%s)", async (ready) => {
diff --git a/server/src/__tests__/environment-routes.test.ts b/server/src/__tests__/environment-routes.test.ts
index c2aa6f0316d..42f5863d1fd 100644
--- a/server/src/__tests__/environment-routes.test.ts
+++ b/server/src/__tests__/environment-routes.test.ts
@@ -13,9 +13,10 @@ const mockAccessService = vi.hoisted(() => ({
 }));
 
 const mockComputerAttach = vi.hoisted(() => vi.fn());
+const mockComputerServiceDb = vi.hoisted(() => vi.fn());
 vi.mock("../modules/computers/index.js", async (importOriginal) => ({
   ...await importOriginal<typeof import("../modules/computers/index.js")>(),
-  computerService: () => ({ attach: mockComputerAttach }),
+  computerService: (db: unknown) => { mockComputerServiceDb(db); return { attach: mockComputerAttach }; },
 }));
 
 const mockAgentService = vi.hoisted(() => ({
@@ -2708,6 +2709,50 @@ describe("environment routes", () => {
     if (!succeeds) expect(mockLogActivity).not.toHaveBeenCalled();
   });
 
+  it.each([false, true])("commits Boat key rotation only after attachment succeeds (%s)", async succeeds => {
+    const priorSecret = "11111111-1111-1111-1111-111111111111";
+    const nextSecret = "22222222-2222-2222-2222-222222222222";
+    let environment = { ...createEnvironment(), driver: "computer", status: "active",
+      config: { provider: "boat", sandboxId: "bx_retained", apiKeySecretRef: { type: "secret_ref", secretId: priorSecret } },
+      metadata: { computerCompanyId: "company-1" } };
+    let boundSecret = priorSecret;
+    let transactionOpen = false;
+    const transaction = vi.spyOn(routeDb, "transaction").mockImplementation(async fn => {
+      const before = environment, bindingBefore = boundSecret;
+      transactionOpen = true;
+      try { return await fn(routeDbTx); }
+      catch (error) { environment = before; boundSecret = bindingBefore; throw error; }
+      finally { transactionOpen = false; }
+    });
+    mockEnvironmentService.getById.mockImplementation(async () => environment);
+    mockEnvironmentService.update.mockImplementation(async (_id, patch) => environment = { ...environment, ...patch });
+    mockSecretService.replaceSecretRefsForInstanceTarget.mockImplementation(async (_target, _refs, options) => {
+      expect(options.db).toBe(routeDbTx);
+      boundSecret = environment.config.apiKeySecretRef.secretId;
+      return [];
+    });
+    mockInstanceSettingsService.getExperimental.mockResolvedValue({ enableBoatEnvironments: true });
+    mockComputerAttach.mockImplementation(async input => {
+      expect(transactionOpen).toBe(true);
+      expect(mockComputerServiceDb).toHaveBeenLastCalledWith(routeDbTx);
+      expect(boundSecret).toBe(nextSecret);
+      expect(input.apiKeySecretRef.secretId).toBe(nextSecret);
+      if (!succeeds) throw conflict("Boat rejected the replacement key");
+      return { computerId: "computer-1" };
+    });
+    try {
+      const app = createApp({ type: "board", userId: "user-1", source: "local_implicit" });
+      const res = await request(app).patch(`/api/environments/${environment.id}`).send({
+        config: { apiKeySecretRef: { type: "secret_ref", secretId: nextSecret } },
+      });
+      expect(res.status, JSON.stringify(res.body)).toBe(succeeds ? 200 : 409);
+      expect(environment.config.apiKeySecretRef.secretId).toBe(succeeds ? nextSecret : priorSecret);
+      expect(boundSecret).toBe(succeeds ? nextSecret : priorSecret);
+      expect(mockComputerAttach).toHaveBeenCalledOnce();
+      if (!succeeds) expect(mockLogActivity).not.toHaveBeenCalled();
+    } finally { transaction.mockRestore(); }
+  });
+
   it("logs a redacted update summary instead of raw config or metadata", async () => {
     const environment = createEnvironment();
     mockEnvironmentService.getById.mockResolvedValue(environment);
diff --git a/server/src/__tests__/workspace-runtime.test.ts b/server/src/__tests__/workspace-runtime.test.ts
index 021523b997b..7290a474b55 100644
--- a/server/src/__tests__/workspace-runtime.test.ts
+++ b/server/src/__tests__/workspace-runtime.test.ts
@@ -9444,6 +9444,19 @@ describe("workspace realization request additionalSources", () => {
     };
   }
 
+  it.each([undefined, "operator/retained"])("round-trips exact-branch intent independently of branch ownership (%s)", existingBranch => {
+    const workspace = buildRealizedWorkspace({ strategy: "git_worktree", branchName: existingBranch ?? "new-task-branch",
+      existingBranch, branchCreatedByRuntime: false });
+    const request = buildWorkspaceRealizationRequest({ adapterType: "codex", companyId: "company-1",
+      environmentId: "environment-1", executionWorkspaceId: null, issueId: "issue-1", heartbeatRunId: "run-1",
+      requestedMode: "isolated_workspace", workspace, workspaceConfig: null });
+    const parsed = readWorkspaceRealizationRequest(JSON.parse(JSON.stringify(request)));
+    expect(parsed?.source.existingBranch).toBe(existingBranch);
+    expect(parsed?.source.branchName).toBe(workspace.branchName);
+    expect(workspace.branchCreatedByRuntime).toBe(false);
+    if (!existingBranch) expect(request.source).not.toHaveProperty("existingBranch");
+  });
+
   it("round-trips additionalSources and runtime provisioning through build/read realization request", () => {
     const workspace = buildRealizedWorkspace({
       additionalWorkspaces: [
diff --git a/server/src/adapters/registry.ts b/server/src/adapters/registry.ts
index f35d9b4b233..c9c13c144f2 100644
--- a/server/src/adapters/registry.ts
+++ b/server/src/adapters/registry.ts
@@ -432,16 +432,19 @@ const paperclipRunnerAdapter: ServerAdapterModule = {
           if (!((os === "Linux" && arch === "x86_64") || (os === "Darwin" && (arch === "arm64" || (profile.acpxAgent !== "grok" && arch === "x86_64"))))) {
             throw new Error(`ACPX ${profile.acpxAgent} requires a qualified Linux x64 or macOS architecture.`);
           }
+          const runtimeUnverified = { code: "acpx_remote_runtime_unverified", level: "warn" as const,
+            message: "The remote platform is supported. Runtime package integrity and readiness must still be verified by the remote runner before launch." };
           if (target.transport === "computer" && profile.acpxAgent === "claude") {
             const hello = await claudeTestEnvironment({ ...context, adapterType: "claude_local",
               config: { ...context.config, engine: "cli", model: profile.model,
                 dangerouslySkipPermissions: context.config.acpxPermissionMode === "approve-all" } });
-            return { ...hello, adapterType: "paperclip_runner" };
+            return { ...hello, adapterType: "paperclip_runner",
+              status: hello.status === "fail" ? "fail" as const : "warn" as const,
+              checks: [...hello.checks, runtimeUnverified] };
           }
           return {
             adapterType: "paperclip_runner", status: "warn" as const, testedAt: new Date().toISOString(),
-            checks: [{ code: "acpx_remote_runtime_unverified", level: "warn" as const,
-              message: "The remote platform is supported. Runtime package integrity and readiness must still be verified by the remote runner before launch." }],
+            checks: [runtimeUnverified],
           };
         }
         const { probeAcpxClaudeInstallation, probeAcpxGrokInstallation, probeAcpxCursorInstallation, probeAcpxPiInstallation } = await import("../vendor/paperclip-runner/live/index.js");
diff --git a/server/src/modules/computers/adapters/boat.test.ts b/server/src/modules/computers/adapters/boat.test.ts
index f2cd70e153d..e7f7c088fa1 100644
--- a/server/src/modules/computers/adapters/boat.test.ts
+++ b/server/src/modules/computers/adapters/boat.test.ts
@@ -771,6 +771,33 @@ process.stdout.write(result.stdout||"");process.stderr.write(result.stderr||"");
     expect(f.call({ ...input, branch: "another-branch" })).toEqual({ error: "conflict" });
     expect(git("-C", result.remoteCwd, "status", "--short")).toContain("preserved");
   });
+  it.each([false, true])("attaches only the exact existing worktree branch (present: %s)", present => {
+    const f = fixture(), checkout = join(f.root, "checkout");
+    mkdirSync(checkout, { recursive: true });
+    const git = (...args: string[]) => {
+      const result = spawnSync("git", args, { cwd: checkout, encoding: "utf8" });
+      if (result.status !== 0) throw new Error(result.stderr);
+      return result.stdout.trim();
+    };
+    git("init");
+    git("-c", "user.name=Test", "-c", "user.email=test@example.com", "commit", "--allow-empty", "-m", "base");
+    const expectedHead = git("rev-parse", "HEAD"), branch = "operator/retained";
+    if (present) git("branch", branch);
+    git("-c", "user.name=Test", "-c", "user.email=test@example.com", "commit", "--allow-empty", "-m", "newer base");
+    const input = { action: "workspace", mode: "worktree", taskId: "existing-task", branch, existingBranch: branch, baseRef: "HEAD" };
+    const result = f.call(input);
+    if (present) {
+      expect(result.remoteCwd).toBe(join(f.root, "tasks", "existing-task"));
+      expect(git("-C", result.remoteCwd, "rev-parse", "HEAD")).toBe(expectedHead);
+      writeFileSync(join(result.remoteCwd, "retained-work"), "keep");
+      expect(f.call(input).remoteCwd).toBe(result.remoteCwd);
+      expect(git("-C", result.remoteCwd, "status", "--short")).toContain("retained-work");
+    } else {
+      expect(result).toEqual({ error: "command_failed" });
+      expect(spawnSync("git", ["show-ref", "--verify", `refs/heads/${branch}`], { cwd: checkout }).status).not.toBe(0);
+      expect(existsSync(join(f.root, "tasks", "existing-task"))).toBe(false);
+    }
+  });
   it("roundtrips binary bytes without interpreting text", () => {
     const f = fixture();
     const bytes = Buffer.from([0, 255, 254, 13, 10, 128]);
diff --git a/server/src/modules/computers/adapters/remote-program.ts b/server/src/modules/computers/adapters/remote-program.ts
index 1d555baab02..638a267a152 100644
--- a/server/src/modules/computers/adapters/remote-program.ts
+++ b/server/src/modules/computers/adapters/remote-program.ts
@@ -71,7 +71,8 @@ if act=='workspace':
   info=os.fstat(workspace_lock.fileno())
   if not stat.S_ISREG(info.st_mode) or info.st_nlink!=1:fail('invalid')
   fcntl.flock(workspace_lock,fcntl.LOCK_EX)
-  repo=p.get('repositoryUrl');branch=p.get('branch');task=p.get('taskId');base_ref=p.get('baseRef')
+  repo=p.get('repositoryUrl');branch=p.get('branch');task=p.get('taskId');base_ref=p.get('baseRef');existing_branch=p.get('existingBranch')
+  if existing_branch and (p.get('mode')!='worktree' or existing_branch!=branch):fail('invalid')
   if base_ref and (base_ref.startswith('-') or '\n' in base_ref):fail('invalid')
   checkout=os.path.join(root,'checkout')
   if repo:
@@ -94,7 +95,10 @@ if act=='workspace':
    if not task:fail('invalid')
    target=os.path.join(root,'tasks',task);os.makedirs(os.path.dirname(target),exist_ok=True)
    task_branch=branch or 'paperclip/task-'+task
-   if not os.path.exists(target):run(['git','worktree','add','-b',task_branch,target,base_ref or 'HEAD'],checkout)
+   if existing_branch:run(['git','show-ref','--verify','refs/heads/'+existing_branch],checkout)
+   if not os.path.exists(target):
+    if existing_branch:run(['git','worktree','add',target,existing_branch],checkout)
+    else:run(['git','worktree','add','-b',task_branch,target,base_ref or 'HEAD'],checkout)
    run(['git','rev-parse','--show-toplevel'],target)
    if run(['git','symbolic-ref','--quiet','--short','HEAD'],target)!=task_branch:fail('conflict')
   else:
diff --git a/server/src/modules/computers/adapters/repository.ts b/server/src/modules/computers/adapters/repository.ts
index 7a827a260f6..6a886a4d4da 100644
--- a/server/src/modules/computers/adapters/repository.ts
+++ b/server/src/modules/computers/adapters/repository.ts
@@ -6,7 +6,8 @@ import {
   type Ledger,
 } from "../domain/ledger.js";
 import type { ComputerRepository } from "../application/ports.js";
-export function computerRepository(db: Db): ComputerRepository {
+export type ComputerDatabase = Db | Parameters<Parameters<Db["transaction"]>[0]>[0];
+export function computerRepository(db: ComputerDatabase): ComputerRepository {
   const decode = (row: typeof computers.$inferSelect): ComputerRecord => ({
     ...row,
     ledger: row.ledger as unknown as Ledger,
diff --git a/server/src/modules/computers/application/service.ts b/server/src/modules/computers/application/service.ts
index 53105fc78fe..8a2d1e85b95 100644
--- a/server/src/modules/computers/application/service.ts
+++ b/server/src/modules/computers/application/service.ts
@@ -901,6 +901,7 @@ finally:
       gitAuth?: { configArgs: string[]; env: Record<string, string> };
       branch?: string;
       baseRef?: string;
+      existingBranch?: string;
       mode: "shared" | "worktree";
     },
   ) {
diff --git a/server/src/modules/computers/index.ts b/server/src/modules/computers/index.ts
index 5ae73890c5a..a352404be51 100644
--- a/server/src/modules/computers/index.ts
+++ b/server/src/modules/computers/index.ts
@@ -1,6 +1,5 @@
-import type { Db } from "@paperclipai/db";
 import { secretService } from "../../services/secrets.js";
-import { computerRepository } from "./adapters/repository.js";
+import { computerRepository, type ComputerDatabase } from "./adapters/repository.js";
 import { boatBackend } from "./adapters/boat.js";
 import { createComputerService } from "./application/service.js";
 export { COMPUTER_RETIREMENT_GRACE_MS, ComputerError, ComputerStopPendingError } from "./domain/ledger.js";
@@ -10,8 +9,8 @@ export type {
 } from "./domain/ledger.js";
 export type ComputerService = ReturnType<typeof createComputerService>;
 export type ComputerBinding = Awaited<ReturnType<ComputerService["admit"]>>;
-const services = new WeakMap<Db, ComputerService>();
-export function computerService(db: Db): ComputerService {
+const services = new WeakMap<ComputerDatabase, ComputerService>();
+export function computerService(db: ComputerDatabase): ComputerService {
   const existing = services.get(db);
   if (existing) return existing;
   const secrets = secretService(db);
diff --git a/server/src/routes/environments.ts b/server/src/routes/environments.ts
index 5794ecc5270..12cacd1e4e3 100644
--- a/server/src/routes/environments.ts
+++ b/server/src/routes/environments.ts
@@ -1252,7 +1252,7 @@ export function environmentRoutes(
     // ref that fails validation (e.g. a deleted secret) must roll the whole
     // save back instead of leaving the config re-pointed with stale bindings.
     let environment = await db.transaction(async (tx) => {
-      const updated = await svc.update(existing.id, patch, { db: tx });
+      let updated = await svc.update(existing.id, patch, { db: tx });
       if (!updated) return null;
       if (patch.config !== undefined || patch.driver !== undefined) {
         await secrets.replaceSecretRefsForInstanceTarget(
@@ -1269,20 +1269,22 @@ export function environmentRoutes(
           { db: tx },
         );
       }
+      // The candidate binding must be visible to provider verification without
+      // retiring the old committed credential when attachment fails. Use this
+      // same transaction for the computer ledger and activation as well.
+      if (updated.driver === "computer" && (req.body.config !== undefined || req.body.status === "active")) {
+        const parsed = parseEnvironmentDriverConfig(updated);
+        if (parsed.driver !== "computer") throw unprocessable("Invalid Boat configuration.");
+        await computerService(tx).attach({ companyId: String(updated.metadata?.computerCompanyId),
+          environmentId: updated.id, sandboxId: parsed.config.sandboxId, apiKeySecretRef: parsed.config.apiKeySecretRef });
+        if (req.body.status !== "archived") updated = (await svc.update(updated.id, { status: "active" }, { db: tx }))!;
+      }
       return updated;
     });
     if (!environment) {
       res.status(404).json({ error: "Environment not found" });
       return;
     }
-    if (environment.driver === "computer" && (req.body.config !== undefined || req.body.status === "active")) {
-      const computerCompanyId = String(environment.metadata?.computerCompanyId);
-      const parsed = parseEnvironmentDriverConfig(environment);
-      if (parsed.driver !== "computer") throw unprocessable("Invalid Boat configuration.");
-      await computerService(db).attach({ companyId: computerCompanyId, environmentId: environment.id,
-        sandboxId: parsed.config.sandboxId, apiKeySecretRef: parsed.config.apiKeySecretRef });
-      if (req.body.status !== "archived") environment = (await svc.update(environment.id, { status: "active" }))!;
-    }
     let customImageReconciliation: Awaited<
       ReturnType<typeof customImages.reconcileActiveTemplateForConfigChange>
     > = { action: "none" };
diff --git a/server/src/services/computer-environment-driver.ts b/server/src/services/computer-environment-driver.ts
index 845a9f0cbd0..5fc754af6e7 100644
--- a/server/src/services/computer-environment-driver.ts
+++ b/server/src/services/computer-environment-driver.ts
@@ -78,13 +78,14 @@ export function createComputerEnvironmentDriver(db: Db): EnvironmentRuntimeDrive
       return { providerLeaseId: lease.providerLeaseId, state: "stopped" };
     },
     async realizeWorkspace({ lease, workspace, gitAuth }) {
-      const request = workspace.metadata?.workspaceRealizationRequest as { source?: { projectId?: string; repoUrl?: string; repoRef?: string; branchName?: string; strategy?: string }; issueId?: string } | undefined;
+      const request = workspace.metadata?.workspaceRealizationRequest as { source?: { projectId?: string; repoUrl?: string; repoRef?: string; branchName?: string; existingBranch?: string; strategy?: string }; issueId?: string } | undefined;
       const result = await computers.realizeWorkspace({ ...scope(lease), owner: computerOwnerFromLease(lease),
         projectId: request?.source?.projectId ?? undefined, taskId: request?.issueId ?? undefined,
         repositoryUrl: request?.source?.repoUrl ?? undefined,
         gitAuth,
         branch: request?.source?.branchName ?? request?.source?.repoRef ?? undefined,
         baseRef: request?.source?.repoRef ?? undefined,
+        existingBranch: request?.source?.existingBranch,
         mode: request?.source?.strategy === "git_worktree" ? "worktree" : "shared" });
       await leases.updateLeaseMetadata(lease.id, { ...lease.metadata, remoteCwd: result.remoteCwd,
         fileAuthority: { kind: "remote-persistent", placementId: result.placementId, root: result.remoteCwd, agentHome: result.agentHome } });
diff --git a/server/src/services/heartbeat/workspace-preparation.test.ts b/server/src/services/heartbeat/workspace-preparation.test.ts
index c251f4e02a9..78d05d30faa 100644
--- a/server/src/services/heartbeat/workspace-preparation.test.ts
+++ b/server/src/services/heartbeat/workspace-preparation.test.ts
@@ -8,6 +8,9 @@ import { eq, sql } from "drizzle-orm";
 import { afterAll, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
 import { getEmbeddedPostgresTestSupport, startEmbeddedPostgresTestDatabase } from "../../__tests__/helpers/embedded-postgres.js";
 import { environmentRunOrchestrator } from "../environment-run-orchestrator.js";
+import { computerService } from "../../modules/computers/index.js";
+import { createComputerEnvironmentDriver } from "../computer-environment-driver.js";
+import { buildWorkspaceRealizationRequest, readWorkspaceRealizationRequest } from "../workspace-realization.js";
 import { environmentService } from "../environments.js";
 import { executionWorkspaceService } from "../execution-workspaces.js";
 import { instanceSettingsService } from "../instance-settings.js";
@@ -219,6 +222,45 @@ describe.skipIf(!support.supported)("heartbeat workspace preparation boundary",
     expect(input.nativeRunnerPreparationSpans).toMatchObject([{ name: "environment.acquire", outcome: "failed" }]);
   });
 
+  it("rejects an existing Boat branch with a shared workspace strategy before acquisition", async () => {
+    const { input, envOrchestrator } = await fixture();
+    input.environment.selectedEnvironmentForConfig = { ...input.environment.selectedEnvironmentForConfig!, driver: "computer" };
+    input.config.mergedConfig = { workspaceStrategy: { type: "project_primary", existingBranch: "operator/retained" } };
+    const acquire = vi.spyOn(envOrchestrator, "acquireForRun");
+    await expect(prepareHeartbeatWorkspace(db, input)).rejects.toMatchObject({
+      resultJson: { workspaceValidation: { reason: "existing_branch_requires_git_worktree" } },
+    });
+    expect(acquire).not.toHaveBeenCalled();
+  });
+
+  it.each([false, true])("preserves Boat workspace base and existing-branch selection (%s)", async existing => {
+    const { input, envOrchestrator } = await fixture(true);
+    input.environment.selectedEnvironmentForConfig = { ...input.environment.selectedEnvironmentForConfig!, driver: "computer" };
+    input.config.mergedConfig = { workspaceStrategy: { type: "git_worktree", baseRef: "release-base",
+      ...(existing ? { existingBranch: "operator/retained" } : {}) } };
+    const stopBeforeRemote = new Error("captured remote realization");
+    const realize = vi.spyOn(envOrchestrator, "realizeForRun").mockRejectedValue(stopBeforeRemote);
+    await expect(prepareHeartbeatWorkspace(db, input)).rejects.toBe(stopBeforeRemote);
+    expect(realize).toHaveBeenCalledOnce();
+    expect(realize.mock.calls[0]![0].executionWorkspace).toMatchObject({
+      repoRef: "release-base", branchName: existing ? "operator/retained" : `paperclip/task-${input.task.issueId}`,
+      branchCreatedByRuntime: false,
+    });
+    const args = realize.mock.calls[0]![0];
+    const request = readWorkspaceRealizationRequest(buildWorkspaceRealizationRequest({ adapterType: input.agent.adapterType,
+      companyId: input.agent.companyId, environmentId: input.environment.selectedEnvironmentId,
+      executionWorkspaceId: null, issueId: input.task.issueId, heartbeatRunId: input.run.id,
+      requestedMode: "isolated_workspace", workspace: args.executionWorkspace, workspaceConfig: null }))!;
+    const remote = vi.spyOn(computerService(db), "realizeWorkspace").mockResolvedValue({
+      remoteCwd: "/home/user/project/task", agentHome: "/home/user/agent", placementId: "placement" });
+    await createComputerEnvironmentDriver(db).realizeWorkspace!({ environment: args.environment,
+      lease: { ...args.lease, providerLeaseId: "owner", metadata: { computerOwner: { computerId: "computer", ownerId: "owner", generation: 1 } } },
+      workspace: { localPath: args.executionWorkspace.cwd, metadata: { workspaceRealizationRequest: request } } });
+    expect(remote).toHaveBeenCalledWith(expect.objectContaining({ baseRef: "release-base",
+      branch: existing ? "operator/retained" : `paperclip/task-${input.task.issueId}`,
+      existingBranch: existing ? "operator/retained" : undefined }));
+  });
+
   it("binds a replacement workspace from realization and snapshots the restore lease", async () => {
     const { input, envOrchestrator, issue } = await fixture();
     const realize = envOrchestrator.realizeForRun;
diff --git a/server/src/services/heartbeat/workspace-preparation.ts b/server/src/services/heartbeat/workspace-preparation.ts
index 39fccda9d68..4fd1ef03738 100644
--- a/server/src/services/heartbeat/workspace-preparation.ts
+++ b/server/src/services/heartbeat/workspace-preparation.ts
@@ -33,6 +33,7 @@ import {
   cleanupExecutionWorkspaceArtifacts,
   ensurePersistedExecutionWorkspaceAvailable,
   realizeExecutionWorkspace,
+  WorkspaceRuntimeValidationFailure,
   type ExecutionWorkspaceInput,
   type RealizedExecutionWorkspace,
 } from "../workspace-runtime.js";
@@ -468,6 +469,14 @@ export async function prepareHeartbeatWorkspace(db: Db, input: HeartbeatWorkspac
       agentId: agent.id,
     },
   );
+  const computerExistingBranch = selectedEnvironmentForConfig?.driver === "computer"
+    ? readNonEmptyString(workspaceStrategyForFingerprint.existingBranch) : null;
+  if (computerExistingBranch && latestWorkspaceStrategyType !== "git_worktree") {
+    throw new WorkspaceRuntimeValidationFailure("An existing branch requires the git_worktree workspace strategy.", {
+      workspaceValidation: { reason: "existing_branch_requires_git_worktree", requestedExistingBranch: computerExistingBranch,
+        strategyType: latestWorkspaceStrategyType },
+    });
+  }
   const {
     executionWorkspace,
     reusedExecutionWorkspace,
@@ -477,8 +486,11 @@ export async function prepareHeartbeatWorkspace(db: Db, input: HeartbeatWorkspac
       ...executionWorkspaceBase,
       strategy: selectedEnvironmentForConfig?.driver === "computer" ? latestWorkspaceStrategyType : "project_primary",
       cwd: resolvedWorkspace.cwd,
+      repoRef: selectedEnvironmentForConfig?.driver === "computer" && latestWorkspaceStrategyType === "git_worktree"
+        ? readNonEmptyString(workspaceStrategyForFingerprint.baseRef) ?? executionWorkspaceBase.repoRef : executionWorkspaceBase.repoRef,
       branchName: selectedEnvironmentForConfig?.driver === "computer" && latestWorkspaceStrategyType === "git_worktree" && issueId
-        ? reusableExistingExecutionWorkspace?.branchName ?? `paperclip/task-${issueId}` : null,
+        ? computerExistingBranch ?? reusableExistingExecutionWorkspace?.branchName ?? `paperclip/task-${issueId}` : null,
+      ...(computerExistingBranch ? { existingBranch: computerExistingBranch } : {}),
       worktreePath: null, warnings: [], created: false, branchCreatedByRuntime: false,
     } as RealizedExecutionWorkspace,
     reusedExecutionWorkspace: false,
diff --git a/server/src/services/workspace-realization.ts b/server/src/services/workspace-realization.ts
index f69e393174e..3569611dc62 100644
--- a/server/src/services/workspace-realization.ts
+++ b/server/src/services/workspace-realization.ts
@@ -93,6 +93,7 @@ export function readWorkspaceRealizationRequest(value: unknown): WorkspaceRealiz
       repoRef: readString(source.repoRef),
       strategy: source.strategy === "git_worktree" ? "git_worktree" : "project_primary",
       branchName: readString(source.branchName),
+      ...(readString(source.existingBranch) ? { existingBranch: readString(source.existingBranch)! } : {}),
       worktreePath: readString(source.worktreePath),
     },
     additionalSources: readAdditionalSources(parsed.additionalSources),
@@ -137,6 +138,7 @@ export function buildWorkspaceRealizationRequest(input: {
       repoRef: input.workspace.repoRef,
       strategy: input.workspace.strategy,
       branchName: input.workspace.branchName,
+      ...(input.workspace.existingBranch ? { existingBranch: input.workspace.existingBranch } : {}),
       worktreePath: input.workspace.worktreePath,
     },
     // The additional (referenced) sources carry the read-only referenced-project workspaces. Run
diff --git a/server/src/services/workspace-runtime.ts b/server/src/services/workspace-runtime.ts
index 5c161536697..64989dfa452 100644
--- a/server/src/services/workspace-runtime.ts
+++ b/server/src/services/workspace-runtime.ts
@@ -170,6 +170,8 @@ export interface RealizedExecutionWorkspace extends ExecutionWorkspaceInput {
   strategy: "project_primary" | "git_worktree";
   cwd: string;
   branchName: string | null;
+  /** Remote realization intent; distinct from ownership established after creation. */
+  existingBranch?: string;
   worktreePath: string | null;
   warnings: string[];
   created: boolean;