Revisit Herdr terminal runtime integration

[devswha]

Context

The fail-closed Herdr terminal runtime integration was proposed in PR #57, which is closed and intentionally deferred from the current release scope. The former branch feat/herdr-terminal-runtime no longer exists on origin. The implementation is preserved by PR #57 at commit 98dbba28a2e50efe71d0562be4629c0ae5a23c9a through refs/pull/57/head.

Resume conditions

• rerun the Phase 0 compatibility probe against the then-current Herdr release
• obtain the independent architecture/security review required by docs/HERDR-PHASE0.md
• update the pinned version, protocol fingerprint, and adversarial evidence if upstream changed
• rerun the full ChatMux verification matrix before reopening or replacing feat(herdr): add fail-closed terminal runtime integration #57

Current preserved state

• PR feat(herdr): add fail-closed terminal runtime integration #57 passed Node 22 and Node 24 CI at the time; that historical evidence does not validate current main or a new Herdr version
• the implementation supports only the measured Herdr v0.7.5/protocol 17 cohort
• unreviewed versions fail closed

No Herdr integration should be merged until the resume conditions above are satisfied.

Recover the preserved implementation

Fetch the pull request ref into a fresh review branch without changing an existing worktree:

git fetch origin refs/pull/57/head:refs/heads/feat/herdr-terminal-runtime-review
git rev-parse feat/herdr-terminal-runtime-review

The expected recovered commit is 98dbba28a2e50efe71d0562be4629c0ae5a23c9a. Review and port any resumed work onto then-current main through a new PR; the compatibility and independent review requirements above remain mandatory.