POC: avoid duplicate Lite workspace refreshes - #15605

🧢 Changes

POC for avoiding duplicate Lite workspace refreshes after mutations.

• Computes an opaque WorkspaceRevision from the semantic inputs used to build the workspace graph.
• Returns the revision with headInfo, mutation responses, and watcher events.
• Updates Lite's existing TanStack Query cache with the mutation result and skips headInfo only when the watcher revision exactly matches it.
• Uses coherence checks and a nullable revision so uncertain or stale reads always fall back to a full refresh.
• Treats Git config, packed-refs, and shallow-boundary changes as unconditional refreshes without reloading the watcher's long-lived repository.
• Adds unit, repository-backed watcher, Electron E2E, benchmark, and temporary diagnostic coverage.

flowchart LR
    M[Lite mutation] --> B[Build workspace + revision]
    B --> C[Cache projection + revision]
    W[Debounced watcher event] --> R[Compute revision]
    R --> E{Matches cached revision?}
    C --> E
    E -->|Yes| S[Keep cached headInfo]
    E -->|No or null| F[Fetch fresh headInfo]

☕️ Reasoning

Filesystem events cannot be reliably correlated with the mutation that caused them. Comparing the resulting semantic state avoids suppressing unrelated external changes while eliminating the common mutation-response/watcher duplicate fetch.

This is intentionally a POC. It keeps the safe existing refresh path whenever equality cannot be proven, does not reload the repository inside the watcher, and includes temporary structured diagnostics for dogfooding. A real-world benchmark with populated forge associations remains follow-up work.