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/types/api.ts

@@ -157,6 +157,20 @@ export interface CaseInfo {
   location?: 'local' | 'linked-local' | 'remote' | 'docker';
   /** Whether this is a linked local folder */
   linked?: boolean;
+  /**
+   * Present when Codeman scaffolded this case directory for an AGENT-spawned session
+   * (the packaged skill's workers, or any spawn naming a parent session), read back
+   * from the case's own marker file — see `src/agent-case-marker.ts`. Absent for every
+   * case a human created, linked or cloned, which is what makes it usable as the
+   * "safe to clean up" signal in the Manage tab.
+   */
+  agentCreated?: {
+    createdAt: string;
+    createdBy: string;
+    parentSessionId?: string;
+    parentSessionName?: string;
+    mode?: string;
+  };
   /** Remote case metadata for display and session creation */
   remote?: {
     hostId: string;
@@ -192,6 +206,25 @@ export interface CaseInfo {
   };
 }
 
+/**
+ * One agent-created case as `GET /api/cases/agent-created` reports it: the cleanup
+ * view over `CaseInfo.agentCreated`, with the two facts a human needs before deleting
+ * a directory — whether an agent is still working in it, and when it was last touched.
+ */
+export interface AgentCaseSummary {
+  name: string;
+  path: string;
+  createdAt: string;
+  createdBy: string;
+  parentSessionId?: string;
+  parentSessionName?: string;
+  mode?: string;
+  /** A live session's working directory is this case — deleting it would pull the rug. */
+  inUse: boolean;
+  /** Directory mtime, so "nothing has touched this in a week" is answerable. */
+  modifiedAt?: string;
+}
+
 // ========== Error Handling Utilities ==========
 
 /**