fix(client): replace a service that failed on an earlier start - #62520

Issue for this PR

Closes #62326

Type of change

• Bug fix

What does this PR do?

ensure() treated a registered service that answers /api/info with 500 as fatal. A boot that fails after registering therefore leaves a process that blocks every later start with Background service failed to start, until someone runs opencode service stop — the state in #62326 and in the triager's reproduction.

The two situations are now separate:

• A failure that happens while this call is starting the service is still reported once, and is not respawned within that call.
• A failure that was already registered before this call started a contender is terminated and replaced, so the next start recovers once the boot cause is gone.

The registration and handoff contracts are unchanged. The Effect and Promise clients are updated together.

How did you verify your code works?

• Fixture tests cover both halves. A pre-registered failed owner is replaced: the old process exits, a new one serves, and onStart reports missing. A service that fails during this call still rejects with Background service failed to start.
• bun test test/service.test.ts test/promise-service.test.ts in packages/client: 43 pass, 4 platform skips, 0 fail.
• bun run typecheck:tsc in packages/client and packages/cli, plus oxlint on the four changed files.
• The POSIX-only lifecycle case "a server that fails to boot reports the failure without respawning" keeps its meaning: the failing call recruits and reports once, so it does not respawn inside that call.

Visual

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Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR