feat(cloud-agent): use readable kilo branch names

[eshurakov]

Summary

• Replace new UUID-based branch defaults with names such as kilo/calm-cedar-az234567, using the existing App Builder-style word generator and an eight-character random suffix.
• Persist the branch at registration so retries and workspace restoration reuse it; preserve explicit and existing branches.
• Fall back to the stored workspace branch in callbacks when no observed branch is available.

Verification

• No manual live-session verification: a live Cloud Agent environment was not started for this narrow backend change.
• Additional manual verification details.

Visual Changes

N/A

Reviewer Notes

• Applies to the agent_* runtime that currently creates UUID-based branches. The control-plane runtime's default-branch behavior is unchanged.
• No new dependencies or migrations. Historical session/ fallbacks remain intact.
• The broader local Workers suite reported 240 passing tests but emitted teardown errors. Focused registration/callback suites completed without teardown errors.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Registration-time kilo/ branch persistence and callback lastSeenBranch fallback look correct on current HEAD, with retries preserving the stored name.

Files Reviewed (6 files)

• services/cloud-agent-next/src/persistence/CloudAgentSession.ts
• services/cloud-agent-next/src/session-service.test.ts
• services/cloud-agent-next/src/session/message-settlement-outbox.test.ts
• services/cloud-agent-next/src/session/message-settlement-outbox.ts
• services/cloud-agent-next/test/integration/session/legacy-callback-enqueue.test.ts
• services/cloud-agent-next/test/integration/session/start-execution-v2.test.ts

Previous Review Summary (commit f79f522)

Current summary above is authoritative. Previous snapshots are kept for context only.

Previous review (commit f79f522)

Status: No Issues Found | Recommendation: Merge

Files Reviewed (6 files)

• services/cloud-agent-next/src/persistence/CloudAgentSession.ts
• services/cloud-agent-next/src/session-service.test.ts
• services/cloud-agent-next/src/session/message-settlement-outbox.test.ts
• services/cloud-agent-next/src/session/message-settlement-outbox.ts
• services/cloud-agent-next/test/integration/session/legacy-callback-enqueue.test.ts
• services/cloud-agent-next/test/integration/session/start-execution-v2.test.ts

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_{Reviewed by grok-4.6 · Input: 198.6K · Output: 14.5K · Cached: 710K}

_{Review guidance: REVIEW.md from base branch main}