Fix FreshOpenCode restart recovery routing

[danshapiro]

Summary:

• Make FreshOpenCode restart recovery route-aware so durable session mutations require the same cwd route.
• Keep recovered no-cwd sessions readable but not mutable, and avoid treating placeholder ids as durable sessions.
• Harden client reconnect state, snapshot invalidation, fake OpenCode route behavior, and terminal retention-loss coalescing.

Verification:

• npm run typecheck
• npm run test:e2e -- test/e2e-browser/specs/freshopencode-restart-recovery.spec.ts
• npm run test:vitest -- --run --config vitest.server.config.ts test/unit/server/fresh-agent/opencode-serve-adapter.test.ts test/unit/server/ws-handler-fresh-agent.test.ts test/unit/server/ws-handler-fresh-agent-lifecycle-parity.test.ts test/server/ws-coding-cli-events.test.ts
• npm run check
• npm run test:status reports full-suite success for 69ffb2c with dirty:0