fix(server): turn diffs keep the agent's files when git's diff.relative is on - #28361

Eligibility
Checkpoint reads now retain repository-relative paths even when Git’s diff.relative setting is enabled, preventing agent edits from disappearing from turn diffs. The overrides apply only to read commands and do not alter Git settings or workspace files.

Additional Thinking

Your Custom Policy

Default risk criteria apply. This restores the existing repository-relative path contract rather than changing a product default; the Git configuration override is command-local. No static-analysis diagnostic suppression is added or broadened, so neither additional human-review condition applies.

Code

Adds command-local diff.relative=false overrides to checkpoint diff and authored-path reads, keeping paths repository-relative for turn summaries and patch selection. Existing path filtering and output limits remain; no repository configuration, working files, or refs are modified by these reads. The ignored file was not reconstructed.

Review Context

Author only21mil is identified; no ownership requirement was supplied. There are no supplied unresolved review comments, correctness findings, or blocking-severity settings. The PR description reports targeted tests and a dev-server reproduction confirming restored agent edits while imported files remain filtered; formal check results were not supplied.

Verdict

The understood change is limited to read-only checkpoint output normalization and its existing display consumers. It leaves persistent Git settings and workspace state unchanged, with no obvious material exposure or product decision requiring human judgment.

Notes:
No code owners found in target merge base 5fe18d7

Agent Credits: 30 credits
Approvability runs at a flat rate of 30 credits whenever the agent is asked for a verdict.