diff --git a/.actrc b/.actrc
deleted file mode 100644
index 69c54909..00000000
--- a/.actrc
+++ /dev/null
@@ -1,3 +0,0 @@
--P ubuntu-latest=catthehacker/ubuntu:act-latest
--P ubuntu-slim=catthehacker/ubuntu:act-latest
---env npm_config_store_dir=/root/.local/share/pnpm/store
diff --git a/.github/workflows/biome.yml b/.github/workflows/biome.yml
index 3c23a47d..41a52470 100644
--- a/.github/workflows/biome.yml
+++ b/.github/workflows/biome.yml
@@ -1,6 +1,11 @@
 name: Biome
 'on':
-  workflow_call: null
+  workflow_call:
+    inputs:
+      since:
+        description: Base commit to compare against. Empty runs everything.
+        type: string
+        default: ''
 permissions:
   contents: read
 jobs:
@@ -10,8 +15,16 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
       - name: Setup workspace
         uses: ./.github/actions/setup
       - name: Lint & format (biome ci)
+        if: inputs.since == ''
         run: pnpm check:ci
+      - name: Lint & format changed files (biome ci)
+        if: inputs.since != ''
+        env:
+          SINCE: ${{ inputs.since }}
+        run: pnpm exec biome ci --changed --since="$SINCE" --no-errors-on-unmatched
     timeout-minutes: 15
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ad551df7..f82cda4f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -13,17 +13,46 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
 jobs:
+  changes:
+    name: Changes
+    runs-on: ubuntu-latest
+    outputs:
+      since: ${{ steps.filter.outputs.everything != 'true' && github.event.pull_request.base.sha || '' }}
+    steps:
+      - uses: actions/checkout@v6
+      - uses: dorny/paths-filter@ceb8a2b8f2d89434be7ff52d3de7ec3738c5cc9d # v4.0.3
+        id: filter
+        if: github.event_name == 'pull_request'
+        with:
+          token: ''
+          filters: |
+            everything:
+              - pnpm-lock.yaml
+              - biome.json
+              - 'tsconfig*.json'
+              - 'mcp-apps/tsconfig.json'
+              - 'vitest*.cts'
+              - '.github/**'
+              - package.json
+    timeout-minutes: 5
   biome:
+    needs: changes
     uses: ./.github/workflows/biome.yml
+    with:
+      since: ${{ needs.changes.outputs.since }}
   typecheck:
     uses: ./.github/workflows/typecheck.yml
   test:
+    needs: changes
     uses: ./.github/workflows/test.yml
+    with:
+      since: ${{ needs.changes.outputs.since }}
   build:
     uses: ./.github/workflows/build.yml
   gate:
     name: CI Gate
     needs:
+      - changes
       - biome
       - typecheck
       - test
@@ -42,6 +71,7 @@ jobs:
   report-failure:
     name: Open issue on main failure
     needs:
+      - changes
       - biome
       - typecheck
       - test
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index eef9e8c9..6a3cc59f 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -1,6 +1,11 @@
 name: Test
 'on':
-  workflow_call: null
+  workflow_call:
+    inputs:
+      since:
+        description: Base commit to compare against. Empty runs everything.
+        type: string
+        default: ''
 permissions:
   contents: read
 jobs:
@@ -10,10 +15,24 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
       - name: Setup workspace
         uses: ./.github/actions/setup
       - name: Run integration tests
+        if: inputs.since == ''
         run: pnpm test:integration
       - name: Run unit tests with the coverage gate
+        if: inputs.since == ''
         run: pnpm test:coverage
+      - name: Run integration tests for changed files
+        if: inputs.since != ''
+        env:
+          SINCE: ${{ inputs.since }}
+        run: pnpm exec vitest run --config vitest.integration.config.cts --changed "$SINCE"
+      - name: Run unit tests for changed files
+        if: inputs.since != ''
+        env:
+          SINCE: ${{ inputs.since }}
+        run: pnpm exec vitest run --changed "$SINCE"
     timeout-minutes: 20
diff --git a/README.md b/README.md
index 52be44cd..52f43f56 100644
--- a/README.md
+++ b/README.md
@@ -701,7 +701,7 @@ pnpm test && pnpm test:integration         # Vitest unit + integration
 pnpm build                                 # Build to build/
 ```
 
-To run the CI gate locally in Docker before pushing, use [act](https://nektosact.com): `act workflow_dispatch -W .github/workflows/ci.yml`. The root `.actrc` picks the runner image and keeps the pnpm store outside the workspace.
+To run the CI gate locally in Docker before pushing, use [act](https://nektosact.com): `act workflow_dispatch -W .github/workflows/ci.yml`. The machine `~/.actrc` selects the runner, architecture and shared caches.
 
 ## Resources
 
diff --git a/biome.json b/biome.json
index 7faf526b..d32c8a8c 100644
--- a/biome.json
+++ b/biome.json
@@ -1,6 +1,6 @@
 {
   "$schema": "https://biomejs.dev/schemas/2.5.1/schema.json",
-  "vcs": { "enabled": true, "clientKind": "git", "useIgnoreFile": true },
+  "vcs": { "enabled": true, "clientKind": "git", "useIgnoreFile": true, "defaultBranch": "main" },
   "files": {
     "ignoreUnknown": true,
     "includes": ["**"]
diff --git a/mcp-apps/tsconfig.json b/mcp-apps/tsconfig.json
index 259c98f3..3208e88f 100644
--- a/mcp-apps/tsconfig.json
+++ b/mcp-apps/tsconfig.json
@@ -6,6 +6,8 @@
     "moduleResolution": "Bundler",
     "jsx": "react-jsx",
     "noEmit": true,
+    "incremental": true,
+    "tsBuildInfoFile": "../node_modules/.cache/tsc/mcp-apps.tsbuildinfo",
     "verbatimModuleSyntax": true,
     "noUnusedLocals": true,
     "noUnusedParameters": true,
diff --git a/package.json b/package.json
index 8fbe1f1d..ccf2bc21 100644
--- a/package.json
+++ b/package.json
@@ -20,9 +20,9 @@
     "skills": "node build/scripts/skills.js",
     "sync": "tsx src/scripts/devSync.ts",
     "diagnose": "node build/scripts/diagnostics.js",
-    "typecheck": "tsc --noEmit",
+    "typecheck": "tsc --noEmit --incremental --tsBuildInfoFile node_modules/.cache/tsc/src.tsbuildinfo",
     "typecheck:mcp-apps": "tsc -p mcp-apps/tsconfig.json --noEmit",
-    "check": "tsc --noEmit && tsc -p mcp-apps/tsconfig.json --noEmit && biome check \"{src,mcp-apps}/**/*.{ts,tsx,js,json,md,css,html}\"",
+    "check": "pnpm run typecheck && pnpm run typecheck:mcp-apps && biome check \"{src,mcp-apps}/**/*.{ts,tsx,js,json,md,css,html}\"",
     "check:ci": "biome ci .",
     "verify": "pnpm run check:ci && pnpm run typecheck && pnpm run typecheck:mcp-apps && pnpm run test && pnpm run build",
     "fix": "biome check --write --no-errors-on-unmatched --files-ignore-unknown=true \"{src,mcp-apps}/**/*.{ts,tsx,js,json,md,css,html}\"",