feat(agent-cases): tag agent-spawned case dirs and sweep their leftovers

A long orchestration creates one case directory per worker and deleting the
sessions never removed them, so ~/codeman-cases accumulated scratch folders
that were indistinguishable from real projects. They are now labelled and
have a cleanup path.

- src/agent-case-marker.ts: a case dir quick-start CREATES for an agent-driven
  spawn gets a .codeman-agent-case.json marker (when, by whom, parent session,
  mode). Only the create branch writes it, so a linked case, a cloned repo or
  any pre-existing path is never labelled; reading is total, so a malformed
  marker means "not agent-created" rather than a half-trusted entry.
- The signal is the new X-Codeman-Agent-Origin header the skill preamble sets
  on its shared curl (preamble bumped to 1.22.0), or an agentOrigin body
  field, falling back to a resolved parentSessionId so a worker spawned by a
  stale skill copy is still labelled.
- GET /api/cases publishes it as agentCreated; GET /api/cases/agent-created is
  a read-only cleanup listing adding inUse and modifiedAt; Add Case -> Manage
  badges each case and offers a review-then-delete sweep that names every
  directory in its confirm and skips any case a live session is working in.
  Removal stays on the existing DELETE /api/cases/:name.
- Agent preamble caches are collected too: ~/.cache/codeman-agent-<id>.sh was
  written per claude session and never removed (236 leftovers measured on a
  working machine). Now deleted with the session and swept at boot, guarded by
  a live-session keep set plus a 7-day age floor.

Verified end to end on an isolated instance: marker written for header, body
and lineage-only spawns, absent with no agent signal and for a pre-existing
directory; inUse flipping on session end; badge, sticky bar, confirm and sweep
driven in a browser; preamble seeded on create, removed on delete, boot sweep
taking only the aged orphans.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/web/routes/session-routes.ts

@@ -76,12 +76,14 @@ import {
   ownerFor,
   parseBody,
   persistAndBroadcastSession,
+  resolveAgentCaseOrigin,
   resolveCasesDir,
   resolveParentSessionId,
   sessionCapacityMessage,
   SETTINGS_PATH,
   validatePathWithinBase,
 } from '../route-helpers.js';
+import { buildAgentCaseMarker, writeAgentCaseMarker } from '../../agent-case-marker.js';
 import { canUsernameRunPrivilegedCommands, resolveClaudeModeForUsername } from '../../user-store.js';
 import { enabledClis, getCli } from '../../config/cli-registry/registry.js';
 import { resolveCliLaunchError } from '../../utils/cli-launcher.js';
@@ -2973,8 +2975,13 @@ export function registerSessionRoutes(
       envOverrides,
       effort,
       parentSessionId,
+      agentOrigin,
     } = parseBody(QuickStartSchema, req.body);
 
+    // Resolved ONCE here: the same value labels a case directory this request creates
+    // (agent-case-marker.ts) and draws the tab lineage line on the session below.
+    const qsParentSessionId = resolveParentSessionId(ctx, req, parentSessionId, owner);
+
     // Multi-user: shell mode is arbitrary host-account execution, gated by the grant.
     // Resolve the owner's grant from the store so a GRANTED regular user is not wrongly denied.
     if (getCli(mode)?.capabilities.privilegedCommandGate && !(await canUsernameRunPrivilegedCommands(owner))) {
@@ -3220,6 +3227,26 @@ export function registerSessionRoutes(
           await writeHooksConfig(resolvedCasePath);
         }
 
+        // Label a directory an AGENT asked us to create, so the scratch workspaces a
+        // long orchestration leaves behind can be told apart from the user's real
+        // projects later (see agent-case-marker.ts). This is the only branch that may
+        // write it: it is the only one that creates the directory, and a pre-existing
+        // case must never be labelled. Best-effort — a failed marker must not fail the
+        // spawn it decorates.
+        const qsAgentOrigin = resolveAgentCaseOrigin(req, agentOrigin, qsParentSessionId);
+        if (qsAgentOrigin) {
+          await writeAgentCaseMarker(
+            resolvedCasePath,
+            buildAgentCaseMarker({
+              createdBy: qsAgentOrigin,
+              parentSessionId: qsParentSessionId,
+              parentSessionName: qsParentSessionId ? ctx.sessions.get(qsParentSessionId)?.name : undefined,
+              mode,
+              owner,
+            })
+          );
+        }
+
         ctx.broadcast(SseEvent.CaseCreated, { name: caseName, path: resolvedCasePath });
       } catch (err) {
         return createErrorResponse(ApiErrorCode.OPERATION_FAILED, `Failed to create case: ${getErrorMessage(err)}`);
@@ -3353,7 +3380,7 @@ export function registerSessionRoutes(
       docker,
       resumeSessionId: dockerResumeId,
       tmuxHistoryLimit: qsTerminalHistoryConfig.tmuxHistoryLimit,
-      parentSessionId: resolveParentSessionId(ctx, req, parentSessionId, owner),
+      parentSessionId: qsParentSessionId,
     });
 
     // Auto-detect completion phrase from CLAUDE.md BEFORE broadcasting