fix(git): cache unsupported capabilities per host (#8109)

* fix(git): cache unsupported capabilities per host

Old Git worktree, ref-search, and merge-tree fallbacks retried unsupported flags on recurring operations, flooding subprocess traces. Centralize capability probing per native, WSL, and SSH execution host, coalesce concurrent probes, and retry periodically for in-place Git upgrades.

* fix(git): recognize real old-Git merge-tree rejection

* test(git): enforce real binary compatibility matrix

* fix(ci): preserve Git compatibility test ownership

* fix(git): retain supported capability state

.github/workflows/pr.yml

@@ -17,7 +17,7 @@ jobs:
         uses: actions/checkout@v6
 
       - name: Install native build tools
-        run: sudo apt-get update && sudo apt-get install -y build-essential python3 zsh
+        run: sudo apt-get update && sudo apt-get install -y build-essential python3 zlib1g-dev zsh
 
       - name: Setup Node.js
         uses: actions/setup-node@v6
@@ -103,6 +103,33 @@ jobs:
       - name: Typecheck
         run: pnpm typecheck
 
+      # Why: real old Git diagnostics differ from mocked errors. Keep the
+      # fallback predicates executable across the baseline, transition, and
+      # current command shapes so a newly added flag cannot silently regress.
+      - name: Verify Git binary compatibility matrix
+        run: |
+          archive="$RUNNER_TEMP/git-2.25.5.tar.gz"
+          source="$RUNNER_TEMP/git-2.25.5"
+          curl -fsSL https://www.kernel.org/pub/software/scm/git/git-2.25.5.tar.gz -o "$archive"
+          echo "41662c52fc16fec4963bfc41075e71f8ead6b5e386797eb6f9a1111ff95a8ddf  $archive" \
+            | sha256sum --check
+          mkdir -p "$source"
+          tar -xzf "$archive" -C "$source" --strip-components=1
+          make -C "$source" -j2 NO_GETTEXT=YesPlease NO_TCLTK=YesPlease NO_PYTHON=YesPlease git
+          ORCA_GIT_COMPAT_BINARY="$source/git" ORCA_GIT_COMPAT_VERSION="2.25.5" \
+            pnpm exec vitest run --config config/vitest.config.ts \
+            src/shared/git-binary-compatibility.test.ts
+
+          for spec in \
+            "alpine/git:edge-2.38.1|2.38.1" \
+            "alpine/git:v2.49.1|2.49.1"; do
+            image="${spec%%|*}"
+            version="${spec#*|}"
+            ORCA_GIT_COMPAT_IMAGE="$image" ORCA_GIT_COMPAT_VERSION="$version" \
+              pnpm exec vitest run --config config/vitest.config.ts \
+              src/shared/git-binary-compatibility.test.ts
+          done
+
       # Why: postinstall rebuilds better-sqlite3 for Electron's ABI via
       # @electron/rebuild, but vitest runs under system Node.js. Rebuild
       # it for Node so orchestration tests can load the native module.