Phase 8: render "Binary file — not displayable" placeholder for binary diffs

[srid]

Why

Phase 8 of #514 lists "binary file diffs" as a robustness gap. The original concrete failure mode (UTF-8-munge of binary content in the diff viewer) was incidentally closed by #708 when it deleted readHeadContent / readWorkingContent and switched to passing git diff output verbatim to Pierre. Today binary files don't crash anything — git diff emits Binary files a/foo and b/foo differ with no @@ hunks, the server returns { hunks: [], … }, and the client renders an empty diff pane.

That's correct behavior, but it's uninformative: an empty pane is indistinguishable from "I clicked a file with no real changes." The user has to dig into the terminal to verify the file is binary and that's why they see nothing.

What ships

A small, independent change. No coupling to #807 or to virtualization.

Server

• packages/integrations/git/src/review.ts — in getDiff, run git diff --numstat <ref> -- <path> alongside the existing git diff call. Numstat reports -\t-\t<path> for binary files (cheap — no extra round trip if we batch with the existing git diff).
• packages/integrations/git/src/schemas.ts — extend GitDiffOutputSchema with binary: boolean (default false). When --numstat reports -\t-\t, set binary: true on the response.
• Streaming endpoints (git.onDiffChange from feat: Code view auto-refreshes from filesystem changes #786) inherit the new field automatically since they re-emit the same schema.

Client

• packages/client/src/ui/PierreDiffView.tsx — when props.binary === true, short-circuit before calling Pierre and render a placeholder panel instead. Suggested copy: "Binary file — not displayable" with a sub-line showing the file's size delta from numstat if available, or just the path. Match the existing empty-state styling in the Code tab.

E2e

• packages/tests/features/code-tab.feature — add scenarios: open a repo with a binary file change (a .png swap or a .wasm rebuild), verify the placeholder renders. Negative case: a no-op file selection still renders an empty pane (not the placeholder), so the two states stay distinguishable.

Out of scope

• Virtualization for large diffs — tracked in Phase 8: wire up Pierre's VirtualizedFileDiff / VirtualizedFile (deferred to #807) #809. Different problem, different wiring, different package (Extract packages/solid-pierre — encapsulate Pierre behind a Solid-native API #807).
• Inline image preview for binary image diffs — interesting future work, but the placeholder ships first; image preview is a separate scope decision (security model, size cap, etc.).
• Rich numstat-only summaries for non-binary files — +12 −7 style. The schema change unblocks this, but it's a different UX feature.

Acceptance

• A binary file in the diff list renders the placeholder instead of an empty pane.
• A no-op file selection still renders an empty pane (we don't regress the "nothing to show" case into a binary placeholder).
• Streaming updates (feat: Code view auto-refreshes from filesystem changes #786) flip the placeholder on/off correctly when a file transitions between binary and text states.

Related

• Code tab: diff review & file browser #514 — Phase 8, binary file diffs line item.
• feat(code-tab): swap file tree + diff view for @pierre/trees and @pierre/diffs #708 — closed the original UTF-8-munge failure mode by removing the byte-read path; this issue closes the leftover UX gap.
• feat: Code view auto-refreshes from filesystem changes #786 — live file watching; the streaming endpoints inherit the binary field automatically once the schema is updated.