test(session):add comprehensive test coverage for resume.go

[StephenJarso]

add comprehensive test coverage for resume.go

Add 34 focused tests for session/resume.go, which previously had no dedicated test file. Tests cover every exported and unexported function:

• SessionFilePath: empty ID rejection, valid path construction
• CompletedCount: nil state, empty items, populated items
• Item: nil state, missing key, found key, defensive copy verification
• ValidateOptions: nil/workspace/empty/missing mode rejection, mode mismatch, range match/mismatch, commit match/mismatch, unsupported mode
• applyResumeLine: session_start, review_item_done (with NewPath fallback and empty fingerprint skip), review_item_reused, review_item_failed (removal + empty fingerprint), unknown type, invalid JSON
• applySessionStart: RepoDir preservation/override, SessionID preservation, all fields set
• copyLlmComments: nil input, empty slice, deep copy with mutation isolation
• LoadResumeState: nonexistent file, empty file, multiple records round-trip, invalid JSON, fail-then-redo replay sequencing

Description

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring (no functional changes)
• Documentation update
• CI / Build / Tooling

How Has This Been Tested?

• make test passes locally
• Manual testing (describe below)

Checklist

• My code follows the project's coding style (go fmt, go vet)
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or my feature works
• New and existing unit tests pass locally with my changes
• I have updated the documentation accordingly (if applicable)
• I have signed the CLA

Related Issues

[CLAassistant]

All committers have signed the CLA.

[github-actions]

✅ OpenCodeReview: No supported files changed.

[StephenJarso]

The tests are running and have followed the contribution guidelines

[lizhengfeng101]

LGTM