feat(ui): unify change comparisons and compact message actions

Branch comparisons could retain an old base or omit local edits, while Changes and walkthrough selected their sources independently.

Share branch and commit selectors across both panels, honor exact refs, include local branch edits, and support first-parent commit diffs with the latest 50 commits. Compact message metadata and move touch actions into a shared sheet.

Validated with workspace type-check, lint and build, focused Git and UI tests, and maintainer testing in the app.

packages/web/server/lib/walkthrough/sources.js

@@ -1,4 +1,4 @@
-import { getDiff, getRangeDiff, getUntrackedDiffs, listUntrackedPaths } from '../git/service.js';
+import { getDiff, getRangeDiff, getCommitDiff, getUntrackedDiffs, listUntrackedPaths } from '../git/service.js';
 
 // A walkthrough source resolves to one or more diff *sections*. A section is a
 // patch plus the scope its hunk ids live in; keeping staged and working-tree
@@ -48,6 +48,18 @@ export function parseSource(raw) {
     return { kind: 'pr', number };
   }
 
+  if (raw.kind === 'commit') {
+    // Sources are content-addressed: accept a full object id, never a moving ref.
+    if (!/^(?:[0-9a-f]{40}|[0-9a-f]{64})$/i.test(raw.hash)) {
+      throw new WalkthroughSourceError('commit sources require a full commit hash');
+    }
+    try {
+      return { kind: 'commit', hash: raw.hash.toLowerCase() };
+    } catch {
+      throw new WalkthroughSourceError('commit sources require a full commit hash');
+    }
+  }
+
   throw new WalkthroughSourceError(`Unknown source kind "${String(raw.kind)}"`);
 }
 
@@ -58,6 +70,7 @@ export function parseSource(raw) {
 export function sourceKey(source) {
   if (source.kind === 'working-tree') return `working-tree:${source.scope}`;
   if (source.kind === 'branch') return `branch:${source.baseRef}...${source.headRef}`;
+  if (source.kind === 'commit') return `commit:${source.hash}`;
   return `pr:${source.number}`;
 }
 
@@ -97,13 +110,21 @@ export async function loadSourceSections(directory, source, { getPullRequestDiff
   }
 
   if (source.kind === 'branch') {
-    const patch = await getRangeDiff(directory, { base: source.baseRef, head: source.headRef });
+    const patch = await getRangeDiff(directory, { base: source.baseRef, head: source.headRef, includeWorkingTree: true });
     return {
       sections: patch && patch.trim() ? [{ scope: 'branch', patch }] : [],
       meta: { baseRef: source.baseRef, headRef: source.headRef },
     };
   }
 
+  if (source.kind === 'commit') {
+    const patch = await getCommitDiff(directory, { hash: source.hash });
+    return {
+      sections: patch.trim() ? [{ scope: 'commit', patch }] : [],
+      meta: { hash: source.hash },
+    };
+  }
+
   if (typeof getPullRequestDiff !== 'function') {
     throw new WalkthroughSourceError('Pull request diffs are unavailable', 500);
   }