Fix review findings: lifecycle containment, configurable tool name, coverage, type catalog

Address four findings from the first Codex review round:

- Contain subagent/start|end listener throws (emitContainedStart/End): a
  thrown lifecycle listener could escape SubagentService.start() before the
  caller received the live run to dispose it (a leaked child), and a thrown
  subagent/end listener could surface as an unhandled rejection on the detached
  result-settle hook. Both emits now log-and-contain, mirroring the agent
  registry's agent/created|disposed containment.
- Make the model-facing tool name configurable (Config.toolName, default
  subagent). The docs say to load dsh-tool-subagent once per provider to expose
  multiple transports, but the hardcoded name made the second load throw a
  duplicate-tool-name error; a distinct toolName per load is now required and
  documented.
- Reach the per-file 100% coverage gate: tests for the subagent/end error
  branch, lifecycle-listener containment, every stopReasonError arm + the
  merge-extensible default, the multi-provider toolName path, agentOptions
  forwarding, and the direct-apply schema-bypass fallbacks.
- Document the seam vocabulary in docs/core-data-structures/subagent.md with
  verbatim type-equiv blocks + manifest entries, and link it from core.md (a
  brand-new core/seam type the doc-sync gate cannot detect on its own).

scripts/type-equiv.manifest.json

@@ -35,6 +35,13 @@
     { "doc": "docs/core-data-structures/bash.md", "symbol": "BashRunResult", "source": "packages/bash/bash/src/types.ts" },
     { "doc": "docs/core-data-structures/bash.md", "symbol": "CollectedOutput", "source": "packages/bash/bash/src/types.ts" },
     { "doc": "docs/core-data-structures/bash.md", "symbol": "BashTask", "source": "packages/bash/bash/src/types.ts" },
-    { "doc": "docs/core-data-structures/bash.md", "symbol": "BashTaskRead", "source": "packages/bash/bash/src/types.ts" }
+    { "doc": "docs/core-data-structures/bash.md", "symbol": "BashTaskRead", "source": "packages/bash/bash/src/types.ts" },
+
+    { "doc": "docs/core-data-structures/subagent.md", "symbol": "SubagentCapabilities", "source": "packages/subagent/subagent/src/types.ts" },
+    { "doc": "docs/core-data-structures/subagent.md", "symbol": "SubagentStartRequest", "source": "packages/subagent/subagent/src/types.ts" },
+    { "doc": "docs/core-data-structures/subagent.md", "symbol": "SubagentResult", "source": "packages/subagent/subagent/src/types.ts" },
+    { "doc": "docs/core-data-structures/subagent.md", "symbol": "SubagentStopReasonMap", "source": "packages/subagent/subagent/src/types.ts" },
+    { "doc": "docs/core-data-structures/subagent.md", "symbol": "SubagentRun", "source": "packages/subagent/subagent/src/types.ts" },
+    { "doc": "docs/core-data-structures/subagent.md", "symbol": "SubagentProvider", "source": "packages/subagent/subagent/src/types.ts" }
   ]
 }