feat(installer): add codegraph uninstall command (#313) (#318)

Adds a cross-channel uninstall that removes CodeGraph from every agent it's
configured on (Claude Code, Cursor, Codex CLI, opencode, Hermes). Prompts
global-vs-local up front (no flags required) and reports which providers it
actually hit; --location / --target / --yes supported for non-interactive use.
Removes only what install wrote; leaves the .codegraph/ index to `uninit`.

Also fixes Cursor uninstall leaving an orphaned .cursor/rules/codegraph.mdc
(its description: CodeGraph frontmatter lingered); the dedicated rules file is
now deleted outright while user content outside our markers is preserved.

Validated end-to-end on macOS and Docker Linux (global + local sweeps clean).
Adds 8 tests; full suite 730 passing. Bumps to 0.9.3 with CHANGELOG entry.

Resolves #313.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/installer/targets/cursor.ts

@@ -46,7 +46,6 @@ import {
   getMcpServerConfig,
   jsonDeepEqual,
   readJsonFile,
-  removeMarkedSection,
   replaceOrAppendMarkedSection,
   writeJsonFile,
 } from './shared';
@@ -140,9 +139,7 @@ class CursorTarget implements AgentTarget {
     }
 
     if (loc === 'local') {
-      const rules = rulesPath();
-      const action = removeMarkedSection(rules, CODEGRAPH_SECTION_START, CODEGRAPH_SECTION_END);
-      files.push({ path: rules, action });
+      files.push(removeRulesEntry());
     }
 
     return { files };
@@ -237,4 +234,57 @@ function writeRulesEntry(): WriteResult['files'][number] {
   return { path: file, action: mapped };
 }
 
+/**
+ * Remove the Cursor rules file on uninstall.
+ *
+ * Unlike the shared CLAUDE.md / AGENTS.md files (where codegraph owns
+ * only a marker-delimited section), `.cursor/rules/codegraph.mdc` is a
+ * file we create OUTRIGHT — the frontmatter is ours too. So a plain
+ * `removeMarkedSection` is wrong here: it would strip our instruction
+ * block but leave the orphaned `description: CodeGraph ...` frontmatter
+ * behind, so the file lingers and still "mentions" codegraph.
+ *
+ * Instead: strip our block, and if nothing but our own frontmatter
+ * remains, delete the whole file. Only when the user has added their
+ * own content outside our markers do we keep the file (minus our block).
+ */
+function removeRulesEntry(): WriteResult['files'][number] {
+  const file = rulesPath();
+  if (!fs.existsSync(file)) return { path: file, action: 'not-found' };
+
+  let content: string;
+  try {
+    content = fs.readFileSync(file, 'utf-8');
+  } catch {
+    return { path: file, action: 'not-found' };
+  }
+
+  const ourFrontmatter = MDC_FRONTMATTER.trim();
+  const startIdx = content.indexOf(CODEGRAPH_SECTION_START);
+  const endIdx = content.indexOf(CODEGRAPH_SECTION_END);
+
+  // Our marked block is present — strip it, then decide what's left.
+  if (startIdx !== -1 && endIdx > startIdx) {
+    const before = content.substring(0, startIdx).trimEnd();
+    const after = content.substring(endIdx + CODEGRAPH_SECTION_END.length).trimStart();
+    const remainder = (before + (before && after ? '\n\n' : '') + after).trim();
+    if (remainder === '' || remainder === ourFrontmatter) {
+      try { fs.unlinkSync(file); } catch { /* ignore */ }
+    } else {
+      atomicWriteFileSync(file, remainder + '\n');
+    }
+    return { path: file, action: 'removed' };
+  }
+
+  // No block, but the file is still our pristine frontmatter-only file
+  // — it's ours, so remove it.
+  if (content.trim() === ourFrontmatter) {
+    try { fs.unlinkSync(file); } catch { /* ignore */ }
+    return { path: file, action: 'removed' };
+  }
+
+  // Foreign content we don't recognize — leave it alone.
+  return { path: file, action: 'not-found' };
+}
+
 export const cursorTarget: AgentTarget = new CursorTarget();