create_session drops the kickoff prompt for new worktree sessions (session created but never starts)

[tclem]

Summary

create_session (the agent tool that provisions a new worktree session with a kickoff.prompt) completes worktree initialization but then silently drops the kickoff: it never spawns the session CLI or dispatches the initial prompt. The session record is persisted (so it shows in the sidebar and get_session returns it), but it sits inert with no CLI process and no turn 0 until something else instantiates it (a send_session_message, or the user opening it in the UI).

From the caller's perspective the session "was created but isn't doing anything."

Impact

Programmatic/agent-driven session creation with an auto-start prompt is unreliable for worktree sessions. A parent agent that spawns a child worktree session to run a task will see the child never start, with no error surfaced back to the tool call.

Evidence (from ~/.copilot/logs/github-app.<pid>.log)

The create_session tool call ran under an external_tool_handler span (request_id=3c1b4564-…). Its full lifecycle in the log:

17:06:16.79  external_tool_handler … initialize_worktree{workspace_id=16ee9915-…}: worktree init progress step="syncing"
17:06:18.45  worktree_sync{base_branch=dev}: git fetch completed
17:06:20.96  worktree_create: create worktree completed branch="tclem-potential-telegram"
17:06:21.00  init: worktree init progress step="ready" Workspace is ready
17:06:21.01  init: workspace initialized successfully workspace_id=16ee9915-…
17:06:21.15  keep_awake: Session became idle (parent session)

…and then nothing for that request. No creating new session, no CLI session created, no kickoff-prompt dispatch, no Session became busy.

Contrast with the parent session's kickoff flow (workspace_branch_kickoff_create_session) earlier in the same log, which is the correct/complete sequence:

branch kickoff: creating session
cli_pool: spawned new CLI process for pool
session::core: CLI session created cli_session_id=…
keep_awake: Session became busy   <-- prompt is now running

The child create_session path performs the worktree half but never reaches the "create CLI session + send kickoff prompt" half.

Confirmation of the lazy/late instantiation:

• First CLI process for the worktree cwd was only spawned at 17:29:57 via workspace_post_complete_warm_cli (pool warm-up triggered by the UI subscribing to the workspace — not the kickoff).
• The actual CLI session (cce2c45b-…) for the worktree wasn't created until 17:30:34, under a different handler — this coincided with a manual send_session_message into the session, which is what finally forced it to run.

So the ~23-minute gap between "session created" and "session actually runs" was entirely because the kickoff never fired; an unrelated message resurrected it.

Expected

When create_session is called with kickoff.prompt, after worktree init succeeds it should proceed to create the session CLI and dispatch the kickoff prompt (matching the workspace_branch_kickoff_create_session flow), so the session starts on its own. If any step fails, the failure should be surfaced back to the tool caller rather than leaving an inert session.

Notes / possibly related

During CLI warm-up and session creation the same log repeatedly emits:

WARN github_app::session::manager::state: failed to fetch models from session CLI for tool descriptions
     context="CLI warm-up" error=invalid type: boolean `true`, expected string or map
WARN github_app::platform::paths: failed to parse /Users/tclem/.copilot/config.json for skillDirectories:
     expected value at line 1 column 1

These look like config/model-list deserialization issues (a boolean where a string/map is expected). Unclear whether related to the dropped kickoff, but flagging in case the kickoff path bails on one of these without logging an error.

Environment

• App: GitHub Copilot app version 0.1.0 (pkg @github/copilot 1.0.61), darwin-arm64
• Session type: worktree (branch workspace), base branch dev
• Repro context: parent session called create_session with kickoff.prompt + mode: autopilot; child worktree session was created but never started until a follow-up message was sent.

Repro (approximate)

1. From an agent session, call create_session for a project, providing kickoff.prompt and a new worktree.
2. Observe the session appears in the sidebar but never takes turn 0 (zero diff, updated_at == created_at, no CLI process).
3. Send any message to the session (or open it in the UI) → it finally spins up a CLI and runs.

  _{Generated via Copilot (Claude Opus 4.8) on behalf of @tclem}