feat: currentAuthor() carries git user.email — fail-open identity (F5 SLICE-2, #14)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/attributionController.ts

@@ -13,6 +13,7 @@ import * as vscode from "vscode";
 import { CoauthorStore } from "./store";
 import { newId, type AttributionRecord, type Provenance } from "./model";
 import { buildFingerprint, resolve, type OffsetRange } from "./anchorer";
+import { gitUserEmail } from "./identity";
 import { applyChange, coalesce, type LiveSpan } from "./attributionTracker";
 import { minimizeReplace, PendingEditRegistry } from "./pendingEdits";
 
@@ -79,7 +80,8 @@ export class AttributionController implements vscode.Disposable {
   }
   private currentAuthor(): Provenance {
     const id = vscode.workspace.getConfiguration("git").get<string>("user.name") || process.env.USER || "human";
-    return { kind: "human", id };
+    const email = gitUserEmail(this.rootDir);
+    return { kind: "human", id, ...(email !== undefined ? { email } : {}) };
   }
   private state(docPath: string): DocAttribution {
     let s = this.docs.get(docPath);

src/identity.ts

@@ -0,0 +1,25 @@
+/**
+ * Cross-rung identity (F5, spec §6.3 fork c): `email` is git's own join key —
+ * forges already map email → account. Resolved from the workspace git config,
+ * cached per root, FAIL-OPEN: absence just omits the optional field and the
+ * sidecar stays valid (spec §6.9). vscode-free, so it is unit-testable.
+ */
+import { execFileSync } from "node:child_process";
+
+const cache = new Map<string, string | undefined>();
+
+export function gitUserEmail(rootDir: string): string | undefined {
+  if (!cache.has(rootDir)) {
+    try {
+      const out = execFileSync("git", ["config", "user.email"], {
+        cwd: rootDir,
+        encoding: "utf8",
+        stdio: ["ignore", "pipe", "ignore"],
+      }).trim();
+      cache.set(rootDir, out || undefined);
+    } catch {
+      cache.set(rootDir, undefined);
+    }
+  }
+  return cache.get(rootDir);
+}

src/threadController.ts

@@ -11,6 +11,7 @@ import * as vscode from "vscode";
 import { CoauthorStore } from "./store";
 import { emptyArtifact, type Artifact, type Provenance } from "./model";
 import { buildFingerprint, resolve, shift, type OffsetRange } from "./anchorer";
+import { gitUserEmail } from "./identity";
 import { addThread, appendMessage, setStatus } from "./threadModel";
 
 /** Test-facing snapshot of what is currently rendered for a document. */
@@ -72,7 +73,8 @@ export class ThreadController implements vscode.Disposable {
 
   private currentAuthor(): Provenance {
     const id = vscode.workspace.getConfiguration("git").get<string>("user.name") || process.env.USER || "human";
-    return { kind: "human", id };
+    const email = gitUserEmail(this.rootDir);
+    return { kind: "human", id, ...(email !== undefined ? { email } : {}) };
   }
 
   private persist(state: DocState): void {

test/identity.test.ts

@@ -0,0 +1,25 @@
+import { describe, it, expect, beforeAll, afterAll } from "vitest";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import { execFileSync } from "node:child_process";
+import { gitUserEmail } from "../src/identity";
+
+let repo: string;
+
+beforeAll(() => {
+  repo = fs.mkdtempSync(path.join(os.tmpdir(), "cowriting-identity-"));
+  execFileSync("git", ["init"], { cwd: repo, stdio: "ignore" });
+  execFileSync("git", ["config", "user.email", "rung@example.org"], { cwd: repo });
+});
+afterAll(() => fs.rmSync(repo, { recursive: true, force: true }));
+
+describe("gitUserEmail (F5 SLICE-2)", () => {
+  it("reads the workspace git config user.email", () => {
+    expect(gitUserEmail(repo)).toBe("rung@example.org");
+  });
+
+  it("fails open (undefined) when git cannot run there", () => {
+    expect(gitUserEmail("/nonexistent-dir-xyz")).toBeUndefined();
+  });
+});