feat(core): reload discovered plugins from source edits - #39174

What

Reload auto-discovered plugin files when their source changes under an existing Config root.

This fixes edits to {plugin,plugins}/*.{ts,js} being observed by the filesystem watcher but suppressed by Config's unchanged Config.Entry[] equality check.

Before / After

Before

1. A user edits .opencode/plugin/local.ts.
2. Config's existing root watcher observes the edit and rediscovers Config entries.
3. The entries are structurally unchanged, so config.updated is not published.
4. PluginSupervisor does not rescan and the old plugin generation remains active.

After

1. The existing Config root watcher publishes the raw path through config.changes().
2. PluginSupervisor accepts paths at or below {plugin,plugins} and coalesces the filesystem burst.
3. The Supervisor rescans plugin operations and activates the changed generation.
4. plugin.updated is published after the new generation is readable.

How

• packages/core/src/plugin/supervisor.ts filters config.changes() with normalized path containment under each active Config directory's plugin and plugins children.
• The predicate intentionally has no suffix check so directory-level filesystem events still invalidate the source set.
• Matching filesystem events receive a generation before the 100 ms debounce, keeping PluginSupervisor.flush aware of accepted startup work.
• Structured Config and SDK plugin updates retain their existing immediate signal path.
• packages/core/test/config/plugin.test.ts removes the synthetic config.updated publication from the existing source-edit test and uses plugin.updated as the read barrier.

Scope

This PR deliberately does not add direct watches for configured local paths outside Config roots. That needs a separate versioned source plan coupling the Config snapshot, resolved entrypoint, watch kind, content revision, activation, and watcher commit.

The Watcher.acquireRelease interruption-safety change is also deferred to a separate PR with focused acquisition, interruption, and teardown coverage.

Testing

• bun test --only-failures test/config/plugin.test.ts --timeout 30000 — 11 passed, 0 failed.
• bun typecheck from packages/core — passed.
• Push hook bun turbo typecheck --concurrency=3 — 32 tasks passed.

Flow

sequenceDiagram
  participant Editor
  participant Config
  participant Supervisor as PluginSupervisor
  participant Registry as Plugin Registry

  Editor->>Config: edit plugin source
  Config->>Supervisor: config.changes(path)
  Supervisor->>Supervisor: filter + debounce + rescan
  Supervisor->>Registry: activate generation
  Registry-->>Supervisor: plugin.updated