/track: one live result of a finite command, refreshed in place (#393)

[raiseCatError]

Stacked on #415 (Semantic Output) → #414 → #413 → #412 → #411. Merge in order. This supersedes draft #394: its scheduler and panel code and its tests are carried here (see below).

What

/track df -h or /track --every 5s -- docker system df:

• Stored once: the command line and one note — what is tracked, where, and that it runs with sh -c and your shell's PATH, not its aliases or functions.
• Drawn live under them, never stored:
  • a status row that says only what is known: first run pending, live · every 5s · updated 13:49:25 · exit 0 · 12 runs, a failing exit, timed out, could not run, paused, no new result for … (stale), refreshing…, stopped;
  • the latest completed result, with a stable height (the largest seen, at most 12 rows). A shorter refresh never moves what is below it; a longer one says how many lines are hidden.
• Derived rows (the flag added for Semantic Output, now generic): find, selection and /copy never include them, and nothing accumulates per refresh.
• Commands: /track copy [N] copies the latest completed result as plain text; refresh (refused while a sample runs, never overlapped), pause, resume, stop [N|all].
• Stopping writes the last result into the transcript once. A window that closes leaves only the stored lines.
• /watch keeps its manager and behavior (Ask, palette and Actions paths unchanged). Both names share one scheduler, and the manager shows both.

Reconciling draft #394

• src/tasks/WatchTasks.ts and src/tasks/WatchPanel.ts are taken from Track live commands with /track (initial slice of #393) #394 as written. Neither file changed on dev since Track live commands with /track (initial slice of #393) #394's base.
  • Hardening: strict cadence parsing (positive, at most 60 min, fails before spawning); refusals for substitutions, background & and heredocs; an exact docker system df allowance; at most 8 active trackers.
  • Capture and lifecycle: UTF-8-safe bounded capture with a truncation flag; timeouts and spawn errors kept visible; completion on stdio close; TERM then KILL with a grace period; copy-latest in the manager.
• tests/track.test.ts from Track live commands with /track (initial slice of #393) #394 is kept. Its alias expectations now include the track flag.
• Track live commands with /track (initial slice of #393) #394's app and slash edits are re-applied by hand. The rest of Track live commands with /track (initial slice of #393) #394 (docs written for an older base) is replaced by docs/development/track-live-command-refresh.md, revised to match what ships.
• Added in v0.21: an environment provider, so samples use the live shell's PATH; sampling(id); the transcript block (OutputBuffer.addTrackBlock, setLiveRows, presenter liveRows); trackBlock.ts; the final result on stop; /track copy.

Ownership

Window-owned, as /watch always has been. Detach or exit stops trackers and their processes, and they are not restarted on reattach. Service-owned scheduling on the #382 supervisor is deferred and documented.

Tests

• track.test.ts:
  • Track live commands with /track (initial slice of #393) #394's 8 tests;
  • truthful status states;
  • stable height (pad shorter results, count hidden lines of longer ones), with hostile text made inert and fitted;
  • in-place replacement with stored lines unchanged and not found by search;
  • clear resets the block.
• trackApp.test.ts (real scheduler and sh):
  • the block and the first result; a refresh replaces the result with no new stored lines;
  • a second refresh is refused while one runs;
  • stop writes the final result exactly once;
  • /watch still opens its manager.
• trackLive.test.ts (real PTY through the binary):
  • the result updates on screen while the shell runs another command;
  • /track copy puts the latest result on a stand-in clipboard;
  • /track stop leaves it, and the saved journal holds the final result once and no earlier refresh.
• 129 related files pass. Two live tests (tmux reattach, built-binary picker) failed only under load with a stale dist; they pass after a rebuild when run alone.

Not verified

Physical terminal checks: docs/testing/v021-physical-qa.md, section 5, not run. Docker examples need a host with Docker.

Refs #393, #394, #410