Branch staging: create → write → review → merge in the app chrome (P6)

[aaltshuler]

Every notebook write previously landed straight on the graph's main branch — live edits against prod with no review step and no undo story. omnigraph-server 0.7+ has first-class branches (copy-on-write forks, three-way all-or-nothing merge with structured conflicts); this slice plumbs them into the web app as session branch staging.

Client facade

createBranch / mergeBranch / deleteBranch / snapshot on Client. mergeBranch returns a discriminated result ({ok, outcome} | {ok: false, conflicts}) — a conflict is an expected outcome of reviewing staged work, and the target is untouched, so callers render it and continue. Includes a raw-body fallback for the SDK bug where ConflictError.mergeConflicts is always undefined (camelCase read of a snake_case error body; present in 0.7.0 and 0.8.0).

Switch = keyed remount with carried state

The session branch is React state above the runtime; switching remounts RuntimeApp with a source targeting the branch (runtime defaultTarget and ServerSource opts stay in lockstep by construction) and the previous snapshot's state as initialState — selections survive the hop. ?branch= follows via replaceState, and the session branch is deliberately distinct from the declared base (CLI --branch / injected config, never the URL param): reloading a shared ?branch=work-x link lands you back ON the working branch while "merge into" still targets the declared base. Zero core-runtime changes.

BranchBar (header chrome)

• Dropdown (refreshes on open — branches created by an agent or another tab appear without a reload), inline New branch prefilled work-<local date> (a 409 name collision means "exists" → switch to it).
• On a working branch, Review & merge: table-level change summary from two /snapshot reads, two-step-confirmed merge (outcome toast on success; the structured conflict list renders on 409 with the base untouched), and delete-to-abandon. Merge never auto-deletes the source branch.
• Divergence detection: table versions are per-lineage counters, so two diverged branches can share a version number with different contents. Deltas therefore compare version + row-count + writer lineage — numeric ties with a different last-writer render as diverged instead of a false "No changes". (Found live: the naive compare disabled a merge that would conflict.)

Verification

• Tests: client 26 → 31, web +7 (delta computation incl. the diverged case, BranchBar flows incl. conflict rendering, config split).
• Live on the RustFS demo (headed): create → chrome + URL follow → writes stay off main (5 vs 3 in-review) → delta review (Task ±0, v10 → v12) → fast-forward merge picked up by main → delete. Conflict path: divergent approve vs reject on the same row → second merge blocked with divergent_update rendered structured, main intact. Prod smoke read-only.
• Row-level diff review is a noted follow-up (needs a server /changes route over the existing Rust diff_between engine).

🤖 Generated with Claude Code

https://claude.ai/code/session_011TrhtF1SiJghJASMWECzBh

Greptile Summary

This PR adds branch staging to the notebook web app. The main changes are:

• Client methods for creating, merging, deleting, and snapshotting branches.
• Web chrome for switching branches, reviewing staged table changes, merging, and abandoning branches.
• Runtime remounting so reads and writes follow the active session branch.
• Config handling that separates the declared base branch from the URL session branch.
• Tests for branch deltas, conflict rendering, merge flow, and config behavior.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.
• Base-only table removals now appear in the review summary.
• Removed-only staged changes keep the merge action available.

Important Files Changed

Filename	Overview
packages/web/src/branch.ts	Computes table-level branch deltas, including base-only tables as removed entries.
packages/web/src/components/BranchBar.tsx	Adds branch switching, staged-change review, merge conflict display, and branch deletion controls.
packages/client/src/http.ts	Adds branch facade methods and snapshot shaping for the web branch workflow.
packages/web/src/config.ts	Separates the declared base branch from the active session branch and exposes source rebuilding.
packages/web/src/App.tsx	Moves branch state above the runtime and remounts the runtime when the active branch changes.

_{Reviews (2): Last reviewed commit: "Delta summary covers base-only tables (s..." | Re-trigger Greptile}

Context used:

• Context used - CLAUDE.md (source)