refactor(core): every registry register-method returns the exact effect disposer

The exact-disposer fix (5fbac8be B1) repaired agents.register but left the
same wrapper (return () => void dispose()) at seven sibling sites:
tools.register, tools.restrict, systemPrompt.section/tools/variable,
agents.setFactory, and subagents.registerProvider. A wrapper makes correct
composite usage unrepresentable — the exact disposer cannot be recovered, so
a generator effect yielding it leaves the inner effect disposing as a
CONCURRENT SIBLING on owner unload, silently reproducing B1's ordering
corruption. The exact disposer serves both usages (composite-nestable AND
fire-and-forget callable); all seven now return it, typed
() => Promise<void> | void, with the convention pinned by a discriminating
test: an async-link composite probe that passes with the exact disposer and
observes the sibling unregistration firing mid-drain with a wrapper.

Re-auditing also surfaced that B1 itself SHIPPED a full-lint failure: it
changed register()'s return type without updating cross-file consumers
(agent.spec.ts dispose() statements, tool-bash's disposer list), which the
staged-scoped pre-commit lint never saw — pnpm run lint was red at HEAD.
Those three sites and this change's own fallout are fixed together: tests
now await disposers (stronger — they observe the full unwind), sync
paths void them, and the two annotation sites carry the honest union type.
agents.register's README line had drifted the same way (B1 updated the
JSDoc, not the README) — all seven README signatures now match; services
catalog regenerated.

packages/bash/tool-bash/tests/tools.spec.ts

@@ -35,7 +35,7 @@ async function setup() {
  * The registration disposer is tracked so {@link unregisterFakeAgents} can drop
  * it (simulating the owning session disconnecting before a task completes).
  */
-const fakeAgentDisposers = new Map<Context, (() => void)[]>()
+const fakeAgentDisposers = new Map<Context, (() => Promise<void> | void)[]>()
 function registerFakeAgent(ctx: Context, sessionId: string, inject: (...args: unknown[]) => void): Agent {
   // The registry KEY (agent.id) is deliberately DIFFERENT from the session
   // token (session.header.id) — a config agent has `agentId !== sessionId`. The
@@ -53,7 +53,7 @@ function registerFakeAgent(ctx: Context, sessionId: string, inject: (...args: un
 
 /** Unregister every fake agent in this ctx (simulate the owning session disconnecting). */
 function unregisterFakeAgents(ctx: Context): void {
-  for (const dispose of fakeAgentDisposers.get(ctx) ?? []) dispose()
+  for (const dispose of fakeAgentDisposers.get(ctx) ?? []) void dispose()
   fakeAgentDisposers.delete(ctx)
 }