Stream background-command output into claude native mirrors

[edwin-zvs]

Problem

Selecting a claude background-task "native" subagent session in the TUI (and webui) session list opened an empty session view. Task-tool subagent mirrors already stream their transcript (projected from subagents/agent-*.jsonl), but background Bash tasks were projected with lifecycle state and title only — no transcript source was wired, so their mirrors had zero events. Since long-running background tasks are what actually stays visible/running in the session list, the empty view is what users hit.

Fix

Claude Code announces each background task's output file in the launch tool_result ("Output is being written to: …/tasks/<id>.output"). The claude adapter now:

• captures the launching Bash command and the announced output path at launch
• tails the output file every watcher tick, projecting into the task's mirror:
  • the command as an opening user message (ordinal 0)
  • output as line-bounded tool messages whose ordinal is the 1-based index of the chunk's last line — deterministic at line granularity, matching the daemon's ordinal replay-dedupe contract
• holds a trailing partial line until its newline arrives (no line split across events), and flushes everything — partial included — when the terminal notification lands
• caps per-tick chunks at 256 KiB so a fast writer drains across ticks instead of producing one enormous event

No daemon or UI changes needed: the existing native-mirror projection persists + broadcasts these events, so the transcript is live in the TUI Chat view and webui.

Latent reconcile bug fixed alongside

The NativeSubagentSnapshot retained-set was derived only from subagents/ dir files, so any snapshot change (an agent child appearing/finishing) would archive a still-running background task's mirror. Live background task ids now count as retained, and a transient read_dir failure no longer emits an authoritative snapshot (which could archive mirrors off bad data). A consequence: the first tick now emits a snapshot even with no children, so stale "running" background mirrors from before a daemon restart get archived on resume — previously they lingered as zombies (the underlying process died with the harness).

Spec 0079 updated with the background-command transcript + retained-set rules.

Verification

• Unit tests: launch→tail registration, output-path parsing (string + array tool_result content), streaming/partial-hold/terminal-flush lifecycle, liveness tracking.
• Full workspace suite: 2715 passed, 0 failed.
• End-to-end against an isolated daemon built from this branch (stub claude, hand-written native transcript): mirror shows the command message, output streams live, the partial line is held until its newline, and the completion notification flushes it and archives the mirror:

--- mirror transcript after first output ---
state: running archived: False
1 {"role": "user", "text": "while sleep 1; do date; done", "type": "message"}
2 {"role": "tool", "text": "tick one\ntick two", "type": "message"}
--- after partial (partial must NOT appear yet) ---
3 {"role": "tool", "text": "tick three", "type": "message"}
--- after completion ---
state: done archived: True title: Tick the clock
4 {"role": "tool", "text": "partial-held", "type": "message"}

Known limitation

On daemon restart + session resume, the root transcript history is skipped, so pre-restart background launches are not re-discovered and their output is not re-tailed — accepted, since the background process itself does not survive the harness restart (its mirror is now correctly archived by the first snapshot instead of lingering as running).

🤖 Generated with Claude Code