fix(mcp): harden connection recovery

[mattzcarey]

Summary

• make per-server retry settings apply when connectToServer() reports a failed connection as a resolved result
• drain connection work under the old id before migrating a server to a stable id
• close connections replaced through the deprecated connect() path and clear their terminated session id from storage

Why

tryN() retries thrown errors, while MCP connection failures are returned as { state: "failed" }. This meant the documented retry budget stopped after one attempt. Separately, stable-id migration could rename a connection while its restore task still addressed the old id, leaving discovery orphaned. Replacing a connection through connect() also dropped the old transport without closing it.

Review follow-up

• connection failures now drive tryN() while authenticating still returns immediately
• migration ignores a rejected background task but waits for all work under the old id to become quiescent, including work registered while an earlier task settles
• migration deliberately has no timeout: renaming while old-id work still runs recreates the orphaned-discovery bug; callers already wait for these same connection attempts in the normal path
• closing a replaced streamable HTTP connection also removes its now-terminated persisted session id
• no verifier findings remain

Validation

• pnpm --filter agents exec vitest run src/tests/mcp — 30 files, 541 tests passed
• pnpm run check — passed
• regression tests cover retry exhaustion/success, OAuth parking, restore-vs-migration ordering, work added during migration, rejected tasks, transport closing, and persisted session cleanup

Includes a patch changeset for agents.

---

[changeset-bot]

🦋 Changeset detected

Latest commit: f1ac7be

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
agents	Patch
@cloudflare/agent-think	Patch

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

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commit: f1ac7be