Fix subagent announce + add promptMode for token efficiency

[tyler6204]

Summary

Fix subagent announce flow (was completely broken) and address all review feedback.

Original Changes

• Fix subagent announce routing and format improvements
• Simplify: main agent summarizes subagent results in its own voice (no extra LLM step)
• Add chat.inject gateway method to inject messages into session transcripts
• Add promptMode to reduce subagent token usage (~25% reduction)
• Expand subagent tool deny list
• Fix session store race condition that caused ~67% of concurrent subagent results to be lost

Review Feedback Fixes

• Fix delete semantics: Replace delete store[key] with store[key] = undefined for merge-safe writes in all 6 flagged locations (legacy alias migrations now work correctly with concurrent writes)
• Add chat.inject bridge handler: Bridge clients can now call chat.inject
• Add tests for merge-delete semantics: 6 new tests covering concurrent writes, deletion via undefined/null, legacy key migration
• Add tests for chat.inject: 4 new tests for append/broadcast path, error cases
• Fix subagent parallelism: Subagents now run in parallel (was serialized due to lane concurrency defaulting to 1, now unlimited by default)
• Add tests for lane concurrency: 2 new tests for Infinity and limited concurrency
• Update docs/types/schema: Reflect new unlimited default for agents.defaults.subagents.maxConcurrent

Session Store Race Condition Fix

When multiple subagents spawn simultaneously, concurrent calls to saveSessionStore would overwrite each other's changes (classic read-modify-write race). Fixed by re-reading the store inside the lock and merging before writing:

await withSessionStoreLock(storePath, async () => {
  const current = loadSessionStore(storePath);  // Re-read inside lock
  const merged = { ...current, ...store };      // Merge (incoming wins)
  // Handle explicit deletions
  for (const key of Object.keys(store)) {
    if (store[key] === undefined || store[key] === null) {
      delete merged[key];
    }
  }
  await saveSessionStoreUnlocked(storePath, merged);
});

Subagent Parallelism Fix

Changed default maxConcurrent from 1 to unlimited (Infinity) in:

• server-lanes.ts (initial apply)
• server-reload-handlers.ts (hot reload)

Users can still cap via agents.defaults.subagents.maxConcurrent config if needed.

Test Plan

• All 3261 tests pass
• Build passes
• Lint clean
• Manual test: spawn subagent, verify main agent summarizes
• Manual test: spawn multiple subagents, verify all run in parallel

🤖 Generated with Claude Code

[steipete]

  Findings

  - High: saveSessionStore now merges inside lock; any top‑level
    delete store[...] no longer removes keys, so alias migrations +
    deletes will resurrect entries. Switch to store[key] = undefined
    (or adjust merge logic) everywhere you delete keys. Refs: src/
    gateway/server-methods/sessions.ts:115, src/gateway/server-
    methods/sessions.ts:164, src/gateway/server-methods/
    sessions.ts:228, src/gateway/server-methods/sessions.ts:303, src/
    gateway/server-bridge-methods-sessions.ts:134, src/gateway/server-
    bridge-methods-sessions.ts:269.
  - Medium: chat.inject added to protocol/server methods but no bridge
    handler → bridge clients can’t call it. Add handler or explicit
    rejection. Ref: src/gateway/server-bridge-methods-chat.ts:32.
  - Low: Missing tests for merge‑delete semantics + chat.inject
    append/broadcast path.

  Questions / assumptions

  - Is chat.inject meant to be bridge‑accessible? If yes, add bridge
    path.

Always do a codex review. You'll be surprised what it finds.

[tyler6204]

Thanks appreciate the feedback, I'll update and check with codex. I also found another issue where subagents appear to be serialized instead of running in parallel. tested by spawning a 30 second wait subagent, then 5 seconds later spawning one that should reply instantly. the instant one didnt start until the slow one finished, confirmed by timestamps. the second subagent showed 0 tokens and empty session while the first was running, then executed right after. will include this fix as well

[tyler6204]

Addressed all review feedback

Fixed:

• ✅ Delete semantics: store[key] = undefined for merge-safe deletes (6 locations)
• ✅ Added chat.inject bridge handler
• ✅ Added tests for merge-delete semantics (6 tests)
• ✅ Added tests for chat.inject (4 tests)
• ✅ Fixed subagent parallelism: now unlimited by default (was serialized due to maxConcurrent: 1)
• ✅ Added tests for lane concurrency (2 tests)

Additional changes:

• Updated docs/types/schema to reflect unlimited default for agents.defaults.subagents.maxConcurrent

All 3261 tests pass, build clean, lint clean. Ready for re-review!

[steipete]

Landed on main with commits: 688a0ce, a4b347b, 10eb1be. Tests: pnpm lint && pnpm build && pnpm test.

[steipete]

Landed on main with commits: 688a0ce, a4b347b, 10eb1be. Tests: pnpm lint && pnpm build && pnpm test.