feat(agent): isolate agent cwd in .ideai/run/<id> to kill convention-file collisions

ARCHITECTURE §14.1: an agent's PTY cwd is now its own
`<project_root>/.ideai/run/<agent-id>/` directory, never the project root, so
N agents of the same profile no longer collide on a single conventional file
(CLAUDE.md/AGENTS.md/...).

- profile: cwd_template is now "{agentRunDir}" (built-in catalogue + docs).
- runtime: resolve_cwd substitutes {agentRunDir} (legacy {projectRoot} kept).
- LaunchAgent: computes + creates the run dir via FileSystem::create_dir_all,
  passes it as the cwd base to the pure prepare_invocation. Contract chosen:
  pass run_dir as the `cwd` argument (no PreparedContext change) — keeps
  prepare_invocation pure, I/O stays in the use case.
- convention file is generated by IdeA inside the run dir via a pure
  compose_convention_file(project_root, agent_md): absolute project-root header
  + agent persona (extensible for skills, §14.2).
- .gitignore: ignore .ideai/run/.
- run-dir cleanup left as a TODO (FileSystem port exposes no delete).

Tests: anti-collision (2 agents -> 2 distinct cwd, 2 distinct convention files,
none at root), run-dir creation order, composed convention file; pure unit
tests for agent_run_dir + compose_convention_file; runtime {agentRunDir}
substitution. cargo test --workspace + clippy -D warnings green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/infrastructure/tests/agent_runtime.rs

@@ -217,15 +217,27 @@ fn prepare_substitutes_project_root_in_cwd_template() {
 }
 
 #[test]
-fn prepare_empty_cwd_template_defaults_to_root() {
+fn prepare_empty_cwd_template_defaults_to_base() {
     let rt = pure_runtime();
     let p = profile(ContextInjection::stdin(), "");
-    let root = ProjectPath::new("/home/me/proj").unwrap();
+    let base = ProjectPath::new("/home/me/proj").unwrap();
 
-    let spec = rt.prepare_invocation(&p, &ctx(), &root).unwrap();
+    let spec = rt.prepare_invocation(&p, &ctx(), &base).unwrap();
     assert_eq!(spec.cwd.as_str(), "/home/me/proj");
 }
 
+#[test]
+fn prepare_substitutes_agent_run_dir_in_cwd_template() {
+    // The canonical template (ARCHITECTURE §14.1): `{agentRunDir}` resolves to the
+    // base cwd the launcher passes — the agent's isolated run directory.
+    let rt = pure_runtime();
+    let p = profile(ContextInjection::convention_file("CLAUDE.md").unwrap(), "{agentRunDir}");
+    let run_dir = ProjectPath::new("/home/me/proj/.ideai/run/agent-1").unwrap();
+
+    let spec = rt.prepare_invocation(&p, &ctx(), &run_dir).unwrap();
+    assert_eq!(spec.cwd.as_str(), "/home/me/proj/.ideai/run/agent-1");
+}
+
 // ---------------------------------------------------------------------------
 // detection_spec (pure)
 // ---------------------------------------------------------------------------