fix(server): Changes totals compare the default branch with its tracking upstream

[abderbejaoui]

When the default branch tracks upstream/main while origin is a lagging fork, Changes can show commits that are already in the tracking upstream. Implicit review previews can use the same wrong base.

Resolve the branch’s qualified remote-tracking ref before falling back to the primary remote. Keep explicit review bases and the existing fallback behavior. This continues @abderbejaoui’s #15393 and the earlier maintainer takeover push, preserving all commits and merging current main normally. Addresses #15314.

Verification on Linux:

• Retained the earlier minimum: one real-repository regression in the existing GitVcsDriverCore test file, one → one case. It covers Changes totals, implicit review preview, and the fallback after removing upstream tracking. Full file: 166/166 pass; the earlier rename/statistics failure no longer reproduces.
• Pinned-main production returns origin/main, +3/−0 for that fixture; the fix returns upstream/main, +0/−0. The regression fails on main and passes after restoring the exact implementation. Negative control · fixed regression.
• Fresh implementation review independently retained the earlier minimal qualified-ref resolver and shortened its comment. Server typecheck and scoped lint/format pass (two existing warnings outside the diff).
• One fresh parallel whole-PR review round with GPT-6 Sol and Claude Opus 5.5 found no confirmed bugs or code blockers. Claude independently repeated the real-Git scenarios and single-file review loading.
• Actual production driver factories from pinned main and this head, using real canonical/fork/checkout repositories, pass seven comparison scenarios: upstream tracking, explicit review base, configured base, local branch/tag shadows, missing tracking ref, local tracking, and no tracking. Each read uses a fresh driver; no Git output or RPC mocks. Before/after output · reproduction script.

This is a server comparison-base fix; screenshots do not add evidence. The real-Git regression exercises the driver APIs rather than a rendered client. macOS, Windows, iOS, Android, Electron desktop, and remote/relay/tunnel sessions were not exercised here. Current-head CI passes and Macroscope approved this exact head; there are no unresolved review threads. Auto-merge is off; this PR remains unmerged.

Earlier maintainer rewrite credited Claude Opus 5.5 tests/review, Claude Fable 5.1 implementation, and GPT-6.1 review. This continuation: GPT-6 Astra tests, GPT-6.1 Sol implementation, GPT-6 Sol and Claude Opus 5.5 adversarial reviews; T3 Code with Codex/Claude harnesses.

[macroscopeapp]

Approvability

Verdict: Approved at 05e25cc

Macroscope's review found this PR approvable — This narrowly fixes Git comparison-base selection so default-branch Changes totals and review previews honor the configured tracking remote instead of assuming the primary remote. The behavior is isolated, preserves fallback behavior, and is covered by an integration regression test.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

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• Plan: Advanced
• Run ID: bf43f689-98c8-41e4-802d-a98cbed53bfe

📥 Commits

Reviewing files that changed from the base of the PR and between 243d1e7 and a4fe801.

📒 Files selected for processing (2)

• apps/server/src/vcs/GitVcsDriverCore.test.ts
• apps/server/src/vcs/GitVcsDriverCore.ts

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📝 Walkthrough

Base-branch selection now prefers the current branch’s tracking upstream when available. If no usable upstream exists, the driver falls back to the matching branch on the primary remote. A test covers both outcomes.

Changes: Git upstream base selection

Layer / File(s)	Summary
Resolve the current branch base apps/server/src/vcs/GitVcsDriverCore.ts, apps/server/src/vcs/GitVcsDriverCore.test.ts	The driver resolves upstream refs for the current or a named branch. Base selection uses the current branch’s tracking ref when available, then falls back to the primary remote. The test checks status and review preview with an upstream, then checks status after that upstream is unset.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: juliusmarminge, t3dotgg

Merge Risk: ⚪ Minimal · up to a4fe8

Default-branch change totals now compare against the branch's tracking upstream and fall back to the primary remote when none exists. No merge-blocking risk was identified.

### Architecture Summary

Architecture risk: 🔵 Low · up to a4fe8

The change affects 1 system.

Changed systems: apps/server

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — apps/server (service) was modified; 2 changed files map to changed impact.

Before / after behavior

• observed — Modified behavior in apps/server/src/vcs/GitVcsDriverCore.test.ts: Adds a test with origin/main behind and upstream/main current and ahead. While main tracks upstream/main, status and review preview use that base and report no changes. After unsetting the upstream, status falls back to origin/main and reports three insertions.
• observed — Modified behavior in apps/server/src/vcs/GitVcsDriverCore.ts: The former resolveCurrentUpstream(cwd) implementation is generalized into resolveUpstreamOf(cwd, refName): null selects @{upstream}, while a branch name selects <branch>@{upstream}. Missing upstream is now detected when the result is empty or still contains @{, replacing the previous exact check for @{upstream}; remote-name parsing remains the same.
• observed — Modified behavior in apps/server/src/vcs/GitVcsDriverCore.ts: For a base-branch candidate matching the current branch with allowRemoteOfCurrent enabled, resolution now checks that branch’s upstream first and returns its remote branch when it exists. If that tracking ref is absent or unresolved, it checks the matching branch on the primary remote as before. Previously this branch only checked the primary remote, so branches tracking another remote now use that tracked copy when available.

Pre-merge checks: 5

Check name	Status	Explanation
Docstring Coverage		No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title is concise, uses the conventional commit format, and accurately describes the primary change: comparing Changes totals with the default branch’s tracking upstream.
Description check		The description clearly explains the problem, implementation, scope, linked issue and PR context, verification results, limitations, and agent attribution. It does not use the template’s section headi…

Full details: Docstring Coverage

Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2 files.

Full details: Description check

Explanation

The description clearly explains the problem, implementation, scope, linked issue and PR context, verification results, limitations, and agent attribution. It does not use the template’s section headings and does not provide a direct maintainer approval comment, but the required information is otherwise substantially complete.

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[juliusmarminge]

Taking over this one. I’ll reduce the tests to the useful coverage, update the implementation against current main, and verify it before publishing the changes.

Dismissing prior approval to re-evaluate 5f94397

[juliusmarminge]

Continuing the existing maintainer takeover for batch worktree-git-05, as requested. I’ll preserve the earlier push, check it against current main, and finish focused verification and fresh reviews here without merging.

Dismissing prior approval to re-evaluate 05e25cc