feat(core): reload commands from config change feed

[kitlangton]

What

Command source invalidation via config.changes: editing, creating, renaming, or deleting Markdown files under a config root's {command,commands} directory now rebuilds command state directly, without waiting for a config.updated event that descendant edits never trigger. Fourth slice of the config source reload series (#38983, #39131, #39157); fixes #37429 for existing config roots (new-root discovery lands later in the series).

How

ConfigCommandPlugin subscribes to the shared config.changes() feed exposed in #39131 and owns its path predicate locally, per the design's ownership split (Config owns topology, domains own which paths matter):

commands/review.md changes
  -> Watcher update flows through config.changes
  -> plugin filter matches is-or-under <root>/{command,commands}
  -> 100ms debounce coalesces bursts
  -> command state rebuilds from inline and Markdown sources
  -> command.updated publishes committed state

• The predicate matches anything at or under <root>/{command,commands} with no file-suffix check, so directory-level events (e.g. mv commands commands-old) that carry no per-file paths still invalidate.
• The subscription forks before the initial scan so an update racing the scan still triggers a rebuild.
• The existing config.updated handler stays for structured config edits (inline commands in opencode.json); both feeds share one reload effect.

Testing

Reworked the source-lifecycle matrix against the renamed services (Command, Bus) using the #39157 fixtures — Config.testLayer provides the entries and Config.Test.emitChange drives the feed, no hand-rolled Watcher stubs:

• Matrix: created / updated / renamed / deleted, each verifying inside the command.updated subscription so the event is asserted as a read barrier (committed state visible at delivery).
• Debounce: three updates in one window produce exactly one rebuild; a later update produces a second (TestClock-driven).
• Isolation: updates outside command source directories produce zero rebuilds, and the feed stays live afterwards.

Tests were red first (all six fail without the fix), then green with it. TestClock note: both Stream.debounce (100ms) and State.reload (500ms batch debounce) register their sleeps from fiber hops a single TestClock.adjust flush can miss, so the tests drive the clock with a settle/adjust loop (advance) that converges deterministically — verified stable across 10 consecutive full-file runs.

bun test test/config/ passes except the pre-existing PluginSupervisor config > reloads an auto-discovered plugin when its file changes failure present on clean base; bun typecheck clean.

Stack

1. test-fixtures
2. feat(core): reload commands from config change feed #39160 👈 current