@@ -8,5 +8,5 @@ PureGate
 purestack-setup
 *.vsix
 .codex/*
-/.tmp
+/.tmp*
 /frontend/out/
@@ -412,6 +412,7 @@ Tracked:
 In dev/watch mode:
 
 - file changes apply incrementally when safe,
+- a page affected by a shared change, such as a header, footer, or navigation edit, renders again on its next request, before it is served,
 - site config changes trigger full rebuild,
 - lazy route render can happen on first request for missing HTML route,
 - live reload is served over SSE (`/__ts-ssg/events`).
 
@@ -4,6 +4,7 @@ import path from 'node:path'
 
 import { disableLogger, getLogger, type Logger } from 'logpot'
 import { afterAll, beforeAll, describe, expect, it } from 'vitest'
+import { makeRepoTempDir } from '../test/repoTempDir'
 
 import {
   type CopyStaticAssetsResult,
@@ -133,9 +134,7 @@ describe('static assets', () => {
   })
 
   it('minifies compiled ts assets when requested', async () => {
-    const root = await fs.mkdtemp(
-      path.join(process.cwd(), '.tmp-ts-ssg-assets-'),
-    )
+    const root = await makeRepoTempDir('.tmp-ts-ssg-assets-')
     const outDir = path.join(root, 'dist')
     try {
       const entryPath = path.join(root, 'login.ts')
@@ -171,9 +170,7 @@ describe('static assets', () => {
   })
 
   it('bundles source-condition packages after stripping unused Regor template tags', async () => {
-    const root = await fs.mkdtemp(
-      path.join(process.cwd(), '.tmp-ts-ssg-assets-'),
-    )
+    const root = await makeRepoTempDir('.tmp-ts-ssg-assets-')
     const outDir = path.join(root, 'dist')
     try {
       await writeFile(
@@ -257,9 +254,7 @@ describe('static assets', () => {
   })
 
   it('removes stale cache-keyed script siblings after writing a new bundle', async () => {
-    const root = await fs.mkdtemp(
-      path.join(process.cwd(), '.tmp-ts-ssg-assets-'),
-    )
+    const root = await makeRepoTempDir('.tmp-ts-ssg-assets-')
     const outDir = path.join(root, 'dist')
     try {
       const entryPath = path.join(root, 'login.ts')
 
@@ -44,6 +44,7 @@ export class IncrementalChangeApplier {
       changedAssets: 0,
       deletedPages: 0,
       deletedAssets: 0,
+      markedPages: 0,
       reason,
     }
   }
@@ -127,14 +128,7 @@ export class IncrementalChangeApplier {
     }
 
     if (this.input.config.navigation.mode !== 'none') {
-      const contentFiles =
-        await this.input.contentState.refreshNavigationAndMarkDirty()
-      await this.input.contentState.rebuildContentRelPaths(
-        contentFiles.map((file) => file.relPath),
-        state.result,
-      )
-      await this.input.persistManifest()
-      return
+      await this.input.contentState.refreshNavigation()
     }
 
     if (state.assetEntry) {
@@ -158,16 +152,15 @@ export class IncrementalChangeApplier {
     signature: FileSignature | null,
   ) {
     if (!signature) {
-      await this.input.contentState.refreshNavigationAndMarkDirty()
+      await this.input.contentState.refreshNavigation()
       await this.input.contentState.removeContentEntryForDeletedSource(
         relPath,
         result,
       )
       return
     }
 
-    const contentFiles =
-      await this.input.contentState.refreshNavigationAndMarkDirty()
+    const contentFiles = await this.input.contentState.refreshNavigation()
     await this.input.contentState.rebuildNavigatedContent({
       contentFiles,
       relPath,
 
@@ -18,6 +18,8 @@ import {
   type BuildContext,
   buildPage,
   renderPageFromFile,
+  resolveHeaderFooterHtml,
+  resolvePagePartials,
   writePage,
   writePageError,
 } from '../page'
@@ -57,6 +59,7 @@ interface RebuildSingleContentInput {
 
 export class IncrementalContentState {
   private readonly dirtyPages = new Set<string>()
+  private markedPages = 0
   private readonly renderInFlight = new Map<string, Promise<boolean>>()
   private readonly contentIndex: ManifestContentIndex
 
@@ -76,6 +79,13 @@ export class IncrementalContentState {
     this.dirtyPages.clear()
   }
 
+  /** Pages marked to render on their next request since the last call. */
+  takeMarkedPageCount() {
+    const count = this.markedPages
+    this.markedPages = 0
+    return count
+  }
+
   async renderAllPages(contentFiles: ResolvedContentFile[], hooks: BuildHooks) {
     let pages = 0
     for (const file of contentFiles) {
@@ -148,17 +158,48 @@ export class IncrementalContentState {
     if (filesChanged) this.markAllPagesDirty(contentRoutes.pages)
   }
 
-  async refreshNavigationAndMarkDirty() {
+  /**
+   * Rebuilds navigation. Every page shows it, so all pages become dirty when
+   * it changes; an edit that leaves it alone touches no other page.
+   */
+  async refreshNavigation() {
+    const { config, context } = this.input
     const contentFiles = await this.refreshContent()
-    this.input.context.navigation = await buildNavigation(
-      this.input.config.contentDir,
+    const navigation = await buildNavigation(
+      config.contentDir,
       contentFiles,
-      this.input.config.navigation,
+      config.navigation,
     )
-    this.markAllPagesDirty(contentFiles)
+    if (JSON.stringify(navigation) !== JSON.stringify(context.navigation)) {
+      context.navigation = navigation
+      this.markAllPagesDirty(contentFiles)
+    }
     return contentFiles
   }
 
+  /**
+   * Compiles the header and footer partials again. Only pages whose nearest
+   * header or footer changed become dirty, so an edit in one folder leaves
+   * pages elsewhere alone.
+   */
+  async refreshPartials() {
+    const { context } = this.input
+    const pages = context.contentRoutes.pages
+    const before = pages.map((page) => resolvePagePartials(context, page))
+    await resolveHeaderFooterHtml(context)
+    this.markPagesDirty(
+      pages
+        .filter((page, index) => {
+          const after = resolvePagePartials(context, page)
+          return (
+            after.headerHtml !== before[index].headerHtml ||
+            after.footerHtml !== before[index].footerHtml
+          )
+        })
+        .map((page) => page.relPath),
+    )
+  }
+
   async removeContentEntryForDeletedSource(
     relPath: string,
     result: IncrementalBuildResult,
@@ -259,11 +300,14 @@ export class IncrementalContentState {
     )
   }
 
-  private markAllPagesDirty(contentFiles: ResolvedContentFile[]) {
+  private markAllPagesDirty(contentFiles: readonly ResolvedContentFile[]) {
     this.dirtyPages.clear()
-    for (const file of contentFiles) {
-      this.dirtyPages.add(file.relPath)
-    }
+    this.markPagesDirty(contentFiles.map((file) => file.relPath))
+  }
+
+  private markPagesDirty(relPaths: readonly string[]) {
+    for (const relPath of relPaths) this.dirtyPages.add(relPath)
+    this.markedPages += relPaths.length
   }
 
   private async renderPageByRelPath(relPath: string, onlyIfDirty: boolean) {
 
@@ -52,44 +52,32 @@ The output is deterministic with `generatedAt` being the only volatile field.
 
 ## `applyChange(filePath)`
 
-Handles a single filesystem change event. It is structured as a fast path with
-early exits:
+Handles a single filesystem change event. The changed page renders right
+away; other affected pages are marked dirty and render on their next request
+(`renderIfDirtyByOutPath`). `IncrementalBuildResult.markedPages` counts them,
+so the dev server can reload the browser.
 
 1. **Ignore changes outside `contentDir`**: relative path starting with `..`.
-2. **Config file change**: if `isSiteConfigFile` ➜ mark `fullRebuild = true`.
-3. **Missing file (deletion)**:
-   - If a content entry exists and navigation is enabled ➜ rebuild navigation
-     for the affected subtree, update manifest, return.
-   - Otherwise delete the output(s), remove manifest entries, update counters.
-4. **Content change**:
-   - If the file is content (or was previously treated as content):
-     - No signature change ➜ no-op.
-     - With navigation enabled ➜ rebuild navigation subtree.
-     - Otherwise rebuild the single page and update its manifest entry.
-5. **Asset change**:
-   - If signature unchanged ➜ no-op.
-   - Otherwise copy static asset, update manifest entry.
-
-The intent is to keep work proportional to the change while preserving
-navigation correctness when navigation is derived from content.
-
-## Navigation-sensitive rebuilds
-
-When navigation is enabled, a single content change can affect:
-
-- The changed page.
-- Its ancestor folders (navigation nodes).
-- Any siblings within the affected folder scope.
-
-`rebuildNavigationForChange` therefore:
-
-1. Re-discovers content and rebuilds the full navigation tree.
-2. Computes affected folders up to `navigationConfig.maxDepth`.
-3. Rebuilds all pages in those folders.
-4. Deletes pages in those folders that no longer exist.
-
-This favors correctness over minimal work whenever navigation structure is
-content-derived.
+2. **`siteConfig.json`** ➜ `fullRebuild = true`. Config shapes every output.
+3. **Header or footer partial** (edit, add, or delete) ➜ compile the partials
+   again and mark only the pages whose nearest header or footer HTML changed.
+4. **`_nav.json`** ➜ rebuild navigation; mark every page only if it changed.
+5. **Content change**: no signature change ➜ no-op. Otherwise render the page,
+   refresh the content index and navigation, and mark pages as below.
+6. **Content deletion**: remove the output and manifest entry, then refresh.
+7. **Asset change**: copy the asset and update its manifest entry. A `.ts`
+   change rebuilds the script bundles that import it.
+
+## What marks other pages
+
+- **Navigation changed** ➜ every page, since every page shows navigation.
+  Navigation is compared as data, so an edit that leaves titles, order, and
+  structure alone marks nothing.
+- **A page or asset was added or removed** ➜ every page, since any content URL
+  may now resolve differently or fail.
+- **A header or footer changed** ➜ the pages that show it.
+- **A script bundle's hashed name changed** ➜ the pages that load it, rendered
+  right away.
 
 ## Manifest assembly