Preserve partial results and definition NDJSON in batch summaries

[Widthdom]

Summary

Batch JSON summaries discarded usable exit-11 query output and serialized multi-row definition NDJSON as escaped stdout. Preserve validated partial rows, terminal metadata and continuation cursors alongside the existing error status, exit code and failure accounting. Normalize definition NDJSON to a stable results array and retain document output for find/definition envelopes.

Partial-output parsing uses the existing capture and JSON-depth limits, reconciles terminal/envelope counts with retained rows, and rejects malformed or conflicting output. Scoped regex find with origin filters also retains partial rows and counts. Verbose/profile diagnostic records are retained without contributing to result counts. Explicit capture/cancellation/timeout errors and unrelated failures keep their typed-error paths. Parent output budgets and input ordering remain enforced.

Validation

• dotnet build -p:UseSharedCompilation=false — zero warnings/errors.
• make lint — full-solution whitespace validation passed.
• Focused batch, child-parser, JSON-envelope, find, definition and CLI-schema regressions on both frameworks: net8.0 269 passed; net9.0 268 passed, one existing skip. This includes the Preserve structured child errors and retry guidance in batch JSON summaries #5259 E028/retry regressions and batch cancellation/timeout coverage.
• New fixtures compare direct and serial/parallel batch output, resume a retained find cursor without gaps or duplicates, and cover count/envelope/zero-row partial output, verbose/profile diagnostic records, definition cardinality/body/output variants, malformed captures and tight parent budgets.
• dotnet run --project tools/CodeIndex.Changelog -- check and git diff --check passed.
• Repository dogfood reproduction preserved five partial find rows with exit 11 and ten structured definition rows. Replaying the batch cursor returned the remaining 21 matches; all 26 match locations equal a complete scan, with no gaps or duplicates. Root and workspace-manifest freshness/completeness checks passed after the post-commit rebuild and index refresh.
• Completed two Codex adversarial-review rounds and addressed all three findings: scoped-find output classification, missing-row/count validation, and diagnostic control records. Direct and serial/parallel regression tests verify the final diagnostic-control fix.

Documentation and changelog

Updated CLI help and the English/Japanese sections of USER_GUIDE.md, DEVELOPER_GUIDE.md, and TESTING_GUIDE.md. Added changelog.d/unreleased/5344.fixed.md; CHANGELOG.md and agent instruction files are unchanged.

Fixes #5344