perf: add Mantis Slack hydrate timings

.github/workflows/mantis-slack-desktop-smoke.yml

@@ -34,6 +34,14 @@ on:
         description: Optional existing Crabbox desktop/browser lease id or slug to reuse
         required: false
         type: string
+      hydrate_mode:
+        description: Remote workspace hydrate mode
+        required: false
+        default: source
+        type: choice
+        options:
+          - source
+          - prehydrated
 
 permissions:
   contents: write
@@ -153,6 +161,16 @@ jobs:
       - name: Build Mantis harness
         run: pnpm build
 
+      - name: Cache Mantis candidate pnpm store
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.local/share/pnpm/store
+            ~/.cache/pnpm
+          key: mantis-slack-pnpm-${{ runner.os }}-${{ env.NODE_VERSION }}-${{ hashFiles('pnpm-lock.yaml') }}
+          restore-keys: |
+            mantis-slack-pnpm-${{ runner.os }}-${{ env.NODE_VERSION }}-
+
       - name: Setup Go for Crabbox CLI
         uses: actions/setup-go@v6
         with:
@@ -185,7 +203,7 @@ jobs:
           worktree_root=".artifacts/qa-e2e/mantis/slack-desktop-smoke-worktrees"
           mkdir -p "$worktree_root"
           git worktree add --detach "$worktree_root/candidate" "$CANDIDATE_SHA"
-          pnpm --dir "$worktree_root/candidate" install --frozen-lockfile
+          pnpm --dir "$worktree_root/candidate" install --frozen-lockfile --prefer-offline
           pnpm --dir "$worktree_root/candidate" build
 
       - name: Run Slack desktop scenario
@@ -205,6 +223,7 @@ jobs:
           CRABBOX_LEASE_ID: ${{ inputs.crabbox_lease_id }}
           CRABBOX_PROVIDER: ${{ inputs.crabbox_provider }}
           KEEP_VM: ${{ inputs.keep_vm }}
+          HYDRATE_MODE: ${{ inputs.hydrate_mode }}
           SCENARIO_ID: ${{ inputs.scenario_id }}
         shell: bash
         run: |
@@ -254,6 +273,7 @@ jobs:
             --credential-source convex \
             --credential-role ci \
             --provider-mode live-frontier \
+            --hydrate-mode "$HYDRATE_MODE" \
             --model openai/gpt-5.4 \
             --alt-model openai/gpt-5.4 \
             --fast \