feat: enable Codex subagent tool calls

[0xSolarPunk]

Summary

• Add an explicit codex-subagent-tool-use shared message contract for official Codex subagent actions.
• Convert Codex JSONL function_call rows and app-server dynamicToolCall rows into the typed message instead of external/unknown tool-use rows.
• Render Codex subagent calls with a first-class Subagent card, result card, and frontend/server contract tests.

Upstream Codex reference

Checked current openai/codex main via GitHub/clone at e0ac5d3c1552b4eb2c11d1f7e215bb933c78ad99.

• Tool specs: https://github.com/openai/codex/blob/main/codex-rs/core/src/tools/handlers/multi_agents_spec.rs
• Tool planning / feature gate: https://github.com/openai/codex/blob/main/codex-rs/core/src/tools/spec_plan.rs
• Config usage hints and defaults: https://github.com/openai/codex/blob/main/codex-rs/core/src/config/mod.rs

This PR does not enable subagent execution in a Codex runtime that lacks the collaboration tools. It makes Garcon typed/render-correct when Codex emits the upstream spawn_agent, send_message, followup_task, wait_agent, interrupt_agent, list_agents, send_input, close_agent, or resume_agent tool calls.

Screenshots

Desktop:

Mobile:

Validation

• bun test server/agents/codex/__tests__/jsonl-tool-use-converter.test.js server/agents/codex/app-server/__tests__/app-server.test.js passes: 52 tests.
• bun run --cwd web test -- src/lib/chat/__tests__/tool-roundtrip.test.ts src/lib/chat/__tests__/tool-display-registry.test.ts src/lib/components/chat/tools/__tests__/ChatToolEventRenderer.test.ts passes: 92 tests.
• bun run check passes: ESLint and Svelte check report 0 errors / 0 warnings.
• bun run start --port 0 builds and starts a throwaway server at http://0.0.0.0:41673; timeout then stops the foreground smoke process.
• bun run test is blocked by the existing Bun environment missing CompressionStream; failures are isolated to server/lib/__tests__/http-compression.test.js compression round-trip/skip-rule cases.

Migration note

Known Codex subagent calls now cross the shared boundary as codex-subagent-tool-use instead of external-tool-use / unknown-tool-use. Frontend behavior resolves by message type and no client path keys off raw provider tool names for this family.

Checklist

• Scope is focused and behavior is covered by tests
• API/WS contract changes include type and test updates

[0xSolarPunk]

Review/fix pass completed. No existing review comments were present. Fixed formatting noise in commit 098b030. Focused validation passed: bun run --cwd web test -- src/lib/chat/__tests__/tool-display-registry.test.ts src/lib/chat/__tests__/tool-roundtrip.test.ts src/lib/components/chat/tools/__tests__/ChatToolEventRenderer.test.ts -> 92 passed. GitHub checks are green again. The stacked dogfood run on #211 also exercises this base renderer path on a separate rebuilt server.