fix(session): recover concatenated session index records

[shizhigu]

Related Issue

Resolve #1925

Problem

When two records in session_index.jsonl lose the newline between them, the reader sends the combined line to JSON.parse and drops both records. SessionStore.get then returns session.not_found even when the session directory is intact.

All current writers append a newline, so the write-side source is still unknown. This change limits recovery to the read path.

What changed

• Keep the single-record JSON.parse fast path. On failure, scan adjacent JSON containers while accounting for nested values, strings, and escapes.
• Apply valid records in file order through the existing path checks. Preserve the complete prefix before damage, then stop at the first untrusted byte.
• Use the same recovery boundary in the v2 reader of the shared legacy index.
• Add core and public SDK regressions plus a patch changeset.

flowchart LR
  A["physical line"] --> B{"single-record parse"}
  B -->|valid| C["validate and apply"]
  B -->|invalid| D["scan adjacent containers"]
  D --> E["apply complete records in order"]
  D -->|damage| F["stop at first untrusted byte"]

Loading

Here A and B are complete JSON records:

Input	Result
A\nB	A, B
AB	A, B
A + truncated B	A
A + garbage + B	A

Recovery is read-only and does not rewrite or reindex the file.

Validation

• Focused recovery tests: 31 passed in v1, 6 passed in v2, including a 150,000-record single-line boundary.
• Full core suites: 3,983 passed in v1 and 3,958 passed in v2.
• SDK resume regression: 8 passed, 1 todo. Full node-sdk suite: 231 passed, 1 todo.
• Typechecks, oxlint, v2 domain lint, changeset status, and git diff --check: passed.

The original Windows write-side trigger was not reproduced. Tests use the missing-separator file shape from the issue.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

🦋 Changeset detected

Latest commit: 490fb8d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@moonshot-ai/kimi-code	Patch

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