[jefft72]

Summary

Adds runtime coverage for prompt admission races around plan continuations, and corrects a plan mode tool expectation that contradicted its own sibling assertion.

Replaces #67.

Reasoning

Prompt admission and session replacement can interleave, and ordering bugs there are easy to introduce and hard to notice.
These tests pin the ordering rather than the implementation, so the coordinator can be refactored without rewriting them.

The plan mode case in the #3592 regression file asserted that leaving plan mode restores only the extension tool, while the assertion thirty lines above it expects the full default set for the same session configuration.
Restoring the full set is the established behaviour, so the expectation was aligned with its sibling rather than the implementation being changed.

Session profile metadata assertions from the original PR are held for the integration stack.

Changes

• Adds runtime coverage for concurrent prompt admission during a plan rebind
• Corrects the plan mode tool restoration expectation in the #3592 regression test
• Removes assertions that depend on session profile metadata

Testing

• npx vitest --run test/suite/agent-session-runtime.test.ts test/suite/regressions/3592-no-builtin-tools-keeps-extension-tools.test.ts
• tsgo --noEmit reports zero errors

[Issacboy123]

LGTM! These tests cover exclusive runtime transitions, routing races, and tool restoration when built-ins are disabled. They also treat accepted-plan routing as distinct from an ordinary prompt. I found no issues during review.