fix(docker): verify the container workdir and end the probe with exit 0

Two defects that only a real container exposes.

The probe chained `command -v X && echo X` with semicolons, and a script's exit
status is its last command's. A container without the last probed CLI made the
whole `sh -lc` exit 1, so a perfectly healthy container with tmux and claude was
reported as "could not exec into the container". A missing CLI is data here, not
failure, so the script now ends with `exit 0`.

containerWorkdir defaulted to hostWorkspacePath. That default holds for an owned
container only because the create-time bind mount puts the host directory at that
exact path; attaching mounts nothing, so the two are independent facts. A host
path absent inside the container makes `docker exec --workdir` fail with an OCI
chdir error that surfaces in the pane as a bare "execvp failed". The preflight now
proves the directory exists inside the container and refuses at link time.

src/docker-hosts.ts

@@ -1084,6 +1084,8 @@ export interface AdoptedContainerProbe {
   tmuxPath?: string;
   /** Modes whose CLI resolved inside the container (`command -v <mode>`). */
   availableModes?: SessionMode[];
+  /** Whether the requested working directory exists INSIDE the container. */
+  workdirExists?: boolean;
   error?: string;
 }
 
@@ -1099,10 +1101,18 @@ export interface AdoptedContainerProbe {
  */
 export async function probeAdoptableContainer(
   docker: Pick<SessionDocker, 'engine' | 'context' | 'daemonHost' | 'containerName'>,
-  modes: SessionMode[] = []
+  modes: SessionMode[] = [],
+  containerWorkdir?: string
 ): Promise<AdoptedContainerProbe> {
   if (IS_TEST_MODE) {
-    return { ok: true, exists: true, running: true, tmuxPath: '/usr/bin/tmux', availableModes: modes };
+    return {
+      ok: true,
+      exists: true,
+      running: true,
+      tmuxPath: '/usr/bin/tmux',
+      availableModes: modes,
+      workdirExists: true,
+    };
   }
   const argv = dockerEngineArgv(docker);
   let running = false;
@@ -1136,7 +1146,19 @@ export async function probeAdoptableContainer(
   // One exec resolves tmux plus every requested CLI, so adoption costs a single
   // round trip. Binaries are fixed mode names, never user input.
   const probes = ['tmux', ...modes.filter((m) => m !== 'shell')];
-  const script = probes.map((bin) => `command -v ${bin} >/dev/null 2>&1 && echo ${bin}`).join('; ');
+  // `; exit 0` is load-bearing: the script's status is its LAST command's, so a
+  // missing final CLI made the whole `sh -lc` exit 1 and the probe reported
+  // "could not exec into the container" for a container that was perfectly fine.
+  // Absence of a CLI is data here, not failure — only a real exec error is.
+  const steps = probes.map((bin) => `command -v ${bin} >/dev/null 2>&1 && echo ${bin}`);
+  // The workdir is checked INSIDE the container, and that is a fact independent
+  // of hostWorkspacePath: an owned container gets the host dir bind-mounted at the
+  // same absolute path at create time, but adoption mounts nothing, so the two
+  // paths only coincide if the user mounted it there themselves. `docker exec
+  // --workdir <missing>` fails with an OCI chdir error the pane surfaces as a bare
+  // "execvp failed", so it is resolved here into an actionable message.
+  if (containerWorkdir) steps.push(`[ -d ${shellescape(containerWorkdir)} ] && echo __workdir__`);
+  const script = `${steps.join('; ')}; exit 0`;
   try {
     const { stdout } = await execFileAsync(
       argv[0],
@@ -1158,6 +1180,17 @@ export async function probeAdoptableContainer(
         error: `container "${docker.containerName}" has no tmux (required for durable sessions; install it inside the container)`,
       };
     }
+    const workdirExists = containerWorkdir ? found.has('__workdir__') : undefined;
+    if (containerWorkdir && !workdirExists) {
+      return {
+        ok: false,
+        exists: true,
+        running: true,
+        image,
+        workdirExists: false,
+        error: `"${containerWorkdir}" does not exist inside container "${docker.containerName}". Adoption mounts nothing, so the container workdir must already exist there — set it to a path inside the container (it need not match the host workspace path).`,
+      };
+    }
     return {
       ok: true,
       exists: true,
@@ -1165,6 +1198,7 @@ export async function probeAdoptableContainer(
       image,
       tmuxPath: 'tmux',
       availableModes: modes.filter((m) => m === 'shell' || found.has(m)),
+      workdirExists,
     };
   } catch (err) {
     const msg = err instanceof Error ? err.message : String(err);

src/web/public/index.html

@@ -2856,6 +2856,11 @@
               <input type="text" id="dockerContainerName" placeholder="my-dev-box" pattern="[a-zA-Z0-9][a-zA-Z0-9_.-]+" autocomplete="off" autocapitalize="off" spellcheck="false">
               <span class="form-hint">Must be running already. <button type="button" class="btn-inline-check" id="dockerAdoptCheckBtn">Check container</button></span>
             </div>
+            <div class="form-row docker-adopt-only">
+              <label>Container Workdir</label>
+              <input type="text" id="dockerAdoptWorkdir" placeholder="/workspace" autocomplete="off" autocapitalize="off" autocorrect="off" spellcheck="false">
+              <span class="form-hint">A path that already exists <em>inside</em> the container. Adoption mounts nothing, so this need not match the host workspace path — leave blank to reuse it only if you mounted it there yourself.</span>
+            </div>
             <div class="form-row">
               <label>Case Name</label>
               <input type="text" id="dockerCaseName" placeholder="sandbox" pattern="[a-zA-Z0-9_-]+" autocomplete="off" autocapitalize="off" spellcheck="false">

src/web/public/session-ui.js

@@ -2975,6 +2975,7 @@ Object.assign(CodemanApp.prototype, {
   async _dockerAdoptPreflight() {
     const statusEl = document.getElementById('dockerLinkStatus');
     const container = document.getElementById('dockerContainerName')?.value.trim();
+    const containerWorkdir = document.getElementById('dockerAdoptWorkdir')?.value.trim();
     const hostId = document.getElementById('dockerHostId').value.trim() || 'local';
     if (!container) {
       if (statusEl) statusEl.textContent = 'Enter a container name first.';
@@ -2986,7 +2987,7 @@ Object.assign(CodemanApp.prototype, {
     const probe = await this._apiJson('/api/docker-cases/adopt-preflight', {
       method: 'POST',
       headers: { 'Content-Type': 'application/json' },
-      body: JSON.stringify({ hostId, container }),
+      body: JSON.stringify({ hostId, container, ...(containerWorkdir ? { containerWorkdir } : {}) }),
     });
     if (!statusEl) return;
     if (!probe) {
@@ -3009,6 +3010,7 @@ Object.assign(CodemanApp.prototype, {
     const hostId = document.getElementById('dockerHostId').value.trim() || 'local';
     const adopting = !!document.getElementById('dockerAdoptExisting')?.checked;
     const container = document.getElementById('dockerContainerName')?.value.trim() || '';
+    const adoptWorkdir = document.getElementById('dockerAdoptWorkdir')?.value.trim() || '';
     const image = document.getElementById('dockerImage').value.trim() || 'codeman/agent:base';
     const network = document.getElementById('dockerNetwork').value;
     const memory = document.getElementById('dockerMemory').value.trim();
@@ -3076,7 +3078,11 @@ Object.assign(CodemanApp.prototype, {
       const caseRes = await fetch(adopting ? '/api/cases/docker-adopt' : '/api/cases/docker-link', {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
-        body: JSON.stringify(adopting ? { name, hostId, hostWorkspacePath, container } : { name, hostId, hostWorkspacePath }),
+        body: JSON.stringify(
+          adopting
+            ? { name, hostId, hostWorkspacePath, container, ...(adoptWorkdir ? { containerWorkdir: adoptWorkdir } : {}) }
+            : { name, hostId, hostWorkspacePath }
+        ),
       });
       const caseData = await caseRes.json();
       if (caseData.success) {

src/web/routes/case-routes.ts

@@ -837,7 +837,15 @@ export function registerCaseRoutes(app: FastifyInstance, ctx: EventPort & Config
           availability.error || 'docker daemon is not available'
         );
       }
-      const probe = await probeAdoptableContainer(toSessionDocker(host, dockerCase), [...DOCKER_ADOPT_PROBE_MODES]);
+      // The container workdir is validated INSIDE the container. It defaults to
+      // hostWorkspacePath only because that is what an owned container's bind
+      // mount guarantees; adoption mounts nothing, so the probe has to prove it.
+      const adoptDocker = toSessionDocker(host, dockerCase);
+      const probe = await probeAdoptableContainer(
+        adoptDocker,
+        [...DOCKER_ADOPT_PROBE_MODES],
+        adoptDocker.containerWorkdir
+      );
       if (!probe.ok) {
         return createErrorResponse(ApiErrorCode.OPERATION_FAILED, probe.error || 'container is not adoptable');
       }
@@ -871,7 +879,8 @@ export function registerCaseRoutes(app: FastifyInstance, ctx: EventPort & Config
         daemonHost: host.daemonHost,
         containerName: body.container,
       },
-      [...DOCKER_ADOPT_PROBE_MODES]
+      [...DOCKER_ADOPT_PROBE_MODES],
+      body.containerWorkdir
     );
     return { success: true, data: probe };
   });

src/web/schemas.ts

@@ -857,6 +857,14 @@ export const DockerAdoptPreflightSchema = z.object({
     .min(2)
     .max(128)
     .regex(/^[a-zA-Z0-9][a-zA-Z0-9_.-]+$/, 'Invalid container name'),
+  /** Optional: also verify this path exists INSIDE the container. */
+  containerWorkdir: z
+    .string()
+    .min(1)
+    .max(2000)
+    .regex(/^\//, 'Container workdir must be absolute')
+    .regex(NO_SHELL_META, 'Invalid characters in container workdir')
+    .optional(),
 });
 
 export const DockerExportSchema = z.object({