feat: choose the initial session mode with ZCODE_ACP_MODE

[jbellis]

Problem

session/create hardcodes mode: "yolo", so every new session starts unrestricted. There is no way to start a session in plan or build without switching after the fact.

Change

ZCODE_ACP_MODE supplies the create-time mode. Unset still means yolo, and the mode dropdown keeps switching modes per session. Values are the backend's own mode ids. The README documents the variable.

Tests

tests/session-lazy.test.ts asserts the default stays yolo and that the variable overrides it.

🤖 Generated with Claude Code

https://claude.ai/code/session_01DLQ3W2owia4SJBvzxSqvVc

[william0wang]

Reviewed (typecheck pass; session-lazy tests 35/35; invalid modes are rejected by the backend with a clear error and resume never clobbers the stored session's mode — both verified).

One small blocking inconsistency: the create-time mode isn't reflected in the session/new response. buildModes() (src/config/options.ts:230-246) returns a hardcoded currentModeId: "yolo" for pending sessions (zcodeSid === null), so a client is told the session is in yolo while it was actually created in ZCODE_ACP_MODE — the stale value stands until the first materialized mode read. Please thread the create-time mode through the pending branch (e.g. seed server.lastMode at create, or pass the env mode as buildModes' pending default).

[jbellis]

Thanks! Addressed in 37e8565 — the create-time mode now lives in a single helper (initialSessionMode() in options.ts) used by the session/create call, buildModes' pending branch, and buildConfigOptions' pending mode currentValue, so session/new advertises the mode the create will actually use (both places had the stale hardcoded value). The lastMode seeding at create follows automatically since it reads buildModes' output.

The existing ZCODE_ACP_MODE test now also asserts the response's currentModeId and the mode configOption's currentValue.

[william0wang]

Verified the fix: typecheck clean, targeted suites green (41/41) — initialSessionMode() as the single source for both the create call and the pending-session advertisement is exactly right.

Same housekeeping as #188: #187's README table reformat leaves this branch conflicting on README.md only (re-insert the ZCODE_ACP_MODE row into the reformatted table). Rebase onto main and I'll merge immediately.

[william0wang]

Landing this directly on main as a1aa2e0 (squash, authorship preserved) for the same reason as #188 — identical content to your branch head, with initialSessionMode() as the single source for create + advertisement. Verified: typecheck clean, full suite 1188/1188. Thanks!