fix: align Runtime Host compatible-change epoch

[Astro-Han]

Summary

Align the Runtime Host compatible-change declaration introduced by #4176 with the current protocol compatibility epoch, 68. This restores the merge-result protocol guard without changing the wire protocol or advancing the epoch.

Root cause

The branch for #4176 created the declaration while its base was at epoch 65. Independent protocol changes advanced main to epoch 68 before #4176 merged.

Git reported no conflict because #4176 did not edit packages/runtime-host/src/protocol/index.ts: the merge result kept main's epoch 68 and added the declaration containing epoch 65. The merge-result guard compares the result with its first parent and requires a newly added compatible-change declaration to match the result's epoch, so it deterministically rejected the mismatched declaration.

This PR changes only the declaration's epoch. It does not modify a wire codec, bump the protocol epoch, change historical result decoding, or add another compatibility path.

Verification

• Before the fix, node scripts/protocol-epoch-check.mjs --base d7efbb478518525c24d8b6dddcde396683ba36a2 --head 8aed381eab3aa429d786a1aafc137fa7163d4e34 exited 2 with Invalid compatible protocol change declaration.
• After the fix, node scripts/protocol-epoch-check.mjs --base d7efbb478518525c24d8b6dddcde396683ba36a2 --head HEAD passed with Protocol added a declared compatible extension at epoch 68.
• node scripts/protocol-epoch-check.mjs --base origin/main --head HEAD passed.
• node --test scripts/protocol-epoch-check.test.mjs passed: 12 tests.
• npx biome format --write packages/runtime-host/protocol-compatible-changes/session-catalog-deep-research-import.json passed with no fixes needed.
• npx biome check packages/runtime-host/protocol-compatible-changes/session-catalog-deep-research-import.json passed.
• git diff --check origin/main...HEAD passed.
• Full-repository tests and typechecks were not run because the change is limited to one guard declaration value.

AI use

Select exactly one:

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Codex traced the merge-result guard and historical persistence boundary, authored the one-line declaration fix, ran focused validation, and drafted this pull request. The commit includes a Generated-by: Codex trailer.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

The protocol guard tests and scoped Biome checks pass; typecheck was not run because no typed source changed.

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No

[ARE404]

Approving fix: align Runtime Host compatible-change epoch at head 5b6b3347.

I verified the one-line fix against the epoch-guard contract:

• packages/runtime-host/protocol-compatible-changes/session-catalog-deep-research-import.json changes epoch from 65 to 68. The guard (protocol-epoch-check.mjs) requires a compatible-change declaration's epoch to exactly equal the current RUNTIME_HOST_COMPATIBILITY_EPOCH (value.epoch !== headEpoch → invalid declaration → files not exempted). On this head the epoch is 68, so 65 was a stale declaration that would have made the guard treat session-catalog.ts / session-continuity.ts as incompatible changes and fail; 68 aligns it and restores the exemption.
• The fix is minimal and numerically correct for this head; the files and reason fields are unchanged.
• test was still settling on the exact head at review time (run 33264696081, in progress); 0 unresolved threads.

No P0–P2.

简体中文

批准 fix: align Runtime Host compatible-change epoch，head 5b6b3347。
对照 epoch-guard 契约核实这一行修复：session-catalog-deep-research-import.json 的 epoch 从 65 改为 68。guard（protocol-epoch-check.mjs）要求 compatible-change 声明的 epoch 必须精确等于当前 RUNTIME_HOST_COMPATIBILITY_EPOCH（value.epoch !== headEpoch → 声明无效 → 文件不被豁免）。本 head 的 epoch 是 68，所以原来的 65 是过期声明，会让 guard 把 session-catalog.ts/session-continuity.ts 当不兼容变更而失败；改成 68 对齐并恢复豁免。修复极简且对本 head 数值正确；files/reason 未动。test 在 exact head 上仍在跑（run 33264696081），approve 时尚未终态；0 未解决线程。无 P0–P2。