[kitlangton]

Why

Stream.debounce forks its upstream pull onto a child fiber via transformPull, so a pipeline that debounces a bus or PubSub stream opens the underlying subscription one fiber hop after Effect.forkScoped({ startImmediately: true }) returns. PubSub does not buffer for future subscribers, so anything published in that hop is dropped. #46843 fixed this in instruction.ts, skill.ts, and tool/mcp.ts by subscribing eagerly and debouncing the already-open subscription; config/plugin/agent.ts and config/plugin/command.ts still debounced a lazy subscription.

Those two sites also had a second hop hiding underneath: they fan in config.changes() and ctx.event.subscribe() with Stream.merge, and Channel.merge forks each side with a scheduled (non-immediate) forkIn. Applying the reference pattern on top of the merged stream therefore still left both subscriptions one hop late (verified: the new test kept failing with that shape). The fix runs each source on its own startImmediately fiber instead of through merge.

What Changes

• packages/core/src/config/plugin/agent.ts: replace Stream.merge(...).pipe(Stream.debounce, runForEach(reload)) with an eager PubSub.sliding<void>(1) feed. config.changes() (filtered to agent sources) and ctx.event.subscribe() (filtered to config.updated) each run Stream.runForEach(notify) forked with startImmediately: true, so both subscriptions open synchronously. The sliding subscription is then Stream.fromSubscription(...).pipe(Stream.debounce("100 millis"), Stream.runForEach(() => reload)). Same 100 ms window, same single serialized reload feed.
• packages/core/src/config/plugin/command.ts: identical restructuring for command sources.
• packages/core/test/config/agent.test.ts, packages/core/test/config/command.test.ts: new case rebuilds on a config update published immediately after startup. It starts the plugin with no directory entries (so startup has no filesystem hop that could mask a late subscription), publishes config.updated through the real Bus in the same fiber step, and requires one reload.

Verification

From packages/core:

• bun typecheck: clean.
• New tests fail deterministically on the unfixed source (condition never became true after 100 advances in advance), both for the original merge + debounce shape and for the intermediate "eager runForEach on the merged stream" shape.
• bun run test test/config/agent.test.ts test/config/command.test.ts --rerun-each 10: 260 pass, 0 fail.
• bun run test (full core suite): 3996 pass, 39 skip, 0 fail.