diff --git a/bin/gstack-gbrain-sync.ts b/bin/gstack-gbrain-sync.ts
index e2ce7a4b..884e7565 100644
--- a/bin/gstack-gbrain-sync.ts
+++ b/bin/gstack-gbrain-sync.ts
@@ -4,29 +4,38 @@
  *
  * Orchestrates three storage tiers per plan §"Storage tiering":
  *
- *   1. Code (current repo)         → gbrain import (Supabase or local PGLite)
+ *   1. Code (current repo)         → `gbrain sources add` (idempotent via
+ *                                    lib/gbrain-sources.ts) + `gbrain sync
+ *                                    --strategy code` (incremental) or
+ *                                    `gbrain reindex-code --yes` (--full).
+ *                                    NEVER `gbrain import` (markdown only).
  *   2. Transcripts + curated memory → gstack-memory-ingest (typed put_page)
  *   3. Curated artifacts to git    → gstack-brain-sync (existing pipeline)
  *
  * Modes:
  *   --incremental (default) — mtime fast-path; runs all 3 stages with cache hits
- *   --full                  — first-run; full walk + import; honest budget per ED2
- *   --dry-run               — preview what would sync; no writes
+ *   --full                  — first-run; full walk + reindex; honest budget per ED2
+ *   --dry-run               — preview what would sync; no writes anywhere (incl. state file)
  *
- * --watch (V1.5 P0 TODO): file-watcher daemon. Deferred per Codex F3 ("no daemon"
- * invariant). For V1, continuous sync rides the preamble-boundary hook only.
+ * Concurrency safety per /plan-eng-review D1:
+ *   - Lock file at ~/.gstack/.sync-gbrain.lock (PID + start ts).
+ *   - Stale-lock takeover after 5 min (process death).
+ *   - State file written via tmp+rename for atomicity.
+ *   - Lock released in finally; SIGINT/SIGTERM trapped for cleanup.
  *
- * Cross-repo TODO (V1.5): when gbrain CLI ships `put_file` + `restore-from-sync`,
- * this helper picks them up via version probe (Codex F6 + D9) and routes
- * code/transcripts to Supabase Storage instead of put_page.
+ * --watch (V1.5 P0 TODO): file-watcher daemon. NOTE: gbrain v0.25.1 already
+ * ships `gbrain sync --watch [--interval N]` and `gbrain sync --install-cron`;
+ * when revisited, /sync-gbrain --watch wires through to the gbrain CLI rather
+ * than building a gstack-side daemon.
  */
 
-import { existsSync, statSync, mkdirSync, writeFileSync, readFileSync } from "fs";
+import { existsSync, statSync, mkdirSync, writeFileSync, readFileSync, unlinkSync, renameSync } from "fs";
 import { join, dirname } from "path";
-import { execSync, spawnSync } from "child_process";
+import { execSync, execFileSync, spawnSync } from "child_process";
 import { homedir } from "os";
 
-import { detectEngineTier, withErrorContext } from "../lib/gstack-memory-helpers";
+import { detectEngineTier, withErrorContext, canonicalizeRemote } from "../lib/gstack-memory-helpers";
+import { sourcePageCount } from "../lib/gbrain-sources";
 
 // ── Types ──────────────────────────────────────────────────────────────────
 
@@ -41,12 +50,22 @@ interface CliArgs {
   codeOnly: boolean;
 }
 
+interface CodeStageDetail {
+  source_id?: string;
+  source_path?: string;
+  page_count?: number | null;
+  last_imported?: string;
+  status?: "ok" | "skipped" | "failed";
+}
+
 interface StageResult {
   name: string;
   ran: boolean;
   ok: boolean;
   duration_ms: number;
   summary: string;
+  /** Stage-specific structured detail. Code stage carries source_id + page_count. */
+  detail?: CodeStageDetail;
 }
 
 // ── Constants ──────────────────────────────────────────────────────────────
@@ -54,6 +73,8 @@ interface StageResult {
 const HOME = homedir();
 const GSTACK_HOME = process.env.GSTACK_HOME || join(HOME, ".gstack");
 const STATE_PATH = join(GSTACK_HOME, ".gbrain-sync-state.json");
+const LOCK_PATH = join(GSTACK_HOME, ".sync-gbrain.lock");
+const STALE_LOCK_MS = 5 * 60 * 1000;
 
 // ── CLI ────────────────────────────────────────────────────────────────────
 
@@ -62,18 +83,18 @@ function printUsage(): void {
 
 Modes:
   --incremental        Default. mtime fast-path; ~50ms steady-state.
-  --full               First-run; full walk + import. Honest ~25-35 min for big Macs (ED2).
-  --dry-run            Preview what would sync; no writes.
+  --full               First-run; full walk + reindex. Honest ~25-35 min for big Macs (ED2).
+  --dry-run            Preview what would sync; no writes anywhere.
 
 Options:
   --quiet              Suppress per-stage output.
-  --no-code            Skip the gbrain import (current repo) stage.
+  --no-code            Skip the cwd code-import stage.
   --no-memory          Skip the gstack-memory-ingest stage (transcripts + artifacts).
   --no-brain-sync      Skip the gstack-brain-sync git pipeline stage.
-  --code-only          Only run the gbrain import stage (alias for --no-memory --no-brain-sync).
+  --code-only          Only run the code-import stage (alias for --no-memory --no-brain-sync).
   --help               This text.
 
-Stages run in order: code import → memory ingest → curated git push.
+Stages run in order: code → memory ingest → curated git push.
 Each stage failure is non-fatal; subsequent stages still run.
 `);
 }
@@ -116,7 +137,7 @@ function parseArgs(): CliArgs {
   return { mode, quiet, noCode, noMemory, noBrainSync, codeOnly };
 }
 
-// ── Stage runners ──────────────────────────────────────────────────────────
+// ── Helpers ────────────────────────────────────────────────────────────────
 
 function repoRoot(): string | null {
   try {
@@ -127,6 +148,32 @@ function repoRoot(): string | null {
   }
 }
 
+function originUrl(): string | null {
+  try {
+    const out = execSync("git remote get-url origin", { encoding: "utf-8", timeout: 2000 });
+    return out.trim();
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Derive a stable source id for the cwd code corpus. Pattern: `gstack-code-<slug>`,
+ * where <slug> comes from canonicalizeRemote() then `/` → `-` (e.g.,
+ * `github.com/garrytan/gstack` → `gstack-code-github-com-garrytan-gstack`).
+ *
+ * Falls back to `gstack-code-<basename(repo)>` when there is no origin (local repo).
+ */
+function deriveCodeSourceId(repoPath: string): string {
+  const remote = canonicalizeRemote(originUrl());
+  if (remote) {
+    return `gstack-code-${remote.replace(/[\/\s]+/g, "-").replace(/-+/g, "-")}`;
+  }
+  // Fallback for repos without a remote.
+  const base = repoPath.split("/").pop() || "repo";
+  return `gstack-code-${base.toLowerCase().replace(/[^a-z0-9-]+/g, "-").replace(/-+/g, "-")}`;
+}
+
 function gbrainAvailable(): boolean {
   try {
     execSync("command -v gbrain", { stdio: "ignore" });
@@ -136,6 +183,55 @@ function gbrainAvailable(): boolean {
   }
 }
 
+// ── Lock file (D1) ─────────────────────────────────────────────────────────
+
+interface LockInfo {
+  pid: number;
+  started_at: string;
+}
+
+function acquireLock(): boolean {
+  mkdirSync(GSTACK_HOME, { recursive: true });
+  if (existsSync(LOCK_PATH)) {
+    // Check if stale.
+    try {
+      const stat = statSync(LOCK_PATH);
+      const ageMs = Date.now() - stat.mtimeMs;
+      if (ageMs > STALE_LOCK_MS) {
+        // Stale; take over.
+        unlinkSync(LOCK_PATH);
+      } else {
+        return false;
+      }
+    } catch {
+      // Cannot stat; bail conservatively.
+      return false;
+    }
+  }
+  const info: LockInfo = { pid: process.pid, started_at: new Date().toISOString() };
+  try {
+    writeFileSync(LOCK_PATH, JSON.stringify(info), { encoding: "utf-8", flag: "wx" });
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+function releaseLock(): void {
+  try {
+    if (!existsSync(LOCK_PATH)) return;
+    const raw = readFileSync(LOCK_PATH, "utf-8");
+    const info = JSON.parse(raw) as LockInfo;
+    if (info.pid === process.pid) {
+      unlinkSync(LOCK_PATH);
+    }
+  } catch {
+    // Best-effort cleanup.
+  }
+}
+
+// ── Stage runners ──────────────────────────────────────────────────────────
+
 function runCodeImport(args: CliArgs): StageResult {
   const t0 = Date.now();
   const root = repoRoot();
@@ -145,42 +241,135 @@ function runCodeImport(args: CliArgs): StageResult {
   if (!gbrainAvailable()) {
     return { name: "code", ran: false, ok: false, duration_ms: 0, summary: "skipped (gbrain CLI not in PATH)" };
   }
+
+  const sourceId = deriveCodeSourceId(root);
+
   if (args.mode === "dry-run") {
-    return { name: "code", ran: false, ok: true, duration_ms: 0, summary: `would: gbrain import ${root} --no-embed` };
-  }
-
-  const importArgs = ["import", root, "--no-embed"];
-  if (args.mode === "incremental") {
-    // gbrain import is itself idempotent on re-import; --incremental flag if it supports
-    importArgs.push("--incremental");
-  }
-
-  try {
-    spawnSync("gbrain", importArgs, {
-      stdio: args.quiet ? ["ignore", "ignore", "ignore"] : ["ignore", "inherit", "inherit"],
-      timeout: 5 * 60 * 1000,
-    });
-    // Trigger background embedding catch-up
-    spawnSync("gbrain", ["embed", "--stale"], {
-      stdio: ["ignore", "ignore", "ignore"],
-      timeout: 1000, // background spawn; don't wait
-    });
     return {
       name: "code",
-      ran: true,
+      ran: false,
       ok: true,
-      duration_ms: Date.now() - t0,
-      summary: `imported ${root}`,
+      duration_ms: 0,
+      summary: `would: gbrain sources add ${sourceId} --path ${root} --federated; gbrain sync --strategy code --source ${sourceId}`,
+      detail: { source_id: sourceId, source_path: root, status: "skipped" },
     };
+  }
+
+  // Step 1: Ensure source registered (idempotent).
+  let registered = false;
+  try {
+    // ensureSourceRegistered is async — but we're in a sync stage runner. Use a deasync pattern.
+    // Bun supports top-level await in main(), but stage runners are sync per orchestrator contract.
+    // Workaround: run as a child Bun script for the registration probe.
+    // Simpler: call gbrain CLI directly via the sync helpers in lib/gbrain-sources.ts probeSource.
+    // For symmetry, we duplicate the small ensureSourceRegistered logic synchronously here using
+    // execFileSync. (The lib helper is preferred for async callers; sync helpers below.)
+    registered = ensureSourceRegisteredSync(sourceId, root);
   } catch (err) {
     return {
       name: "code",
       ran: true,
       ok: false,
       duration_ms: Date.now() - t0,
-      summary: `gbrain import failed: ${(err as Error).message}`,
+      summary: `source registration failed: ${(err as Error).message}`,
+      detail: { source_id: sourceId, source_path: root, status: "failed" },
     };
   }
+
+  // Step 2: Run sync or reindex.
+  const syncArgs = args.mode === "full"
+    ? ["reindex-code", "--source", sourceId, "--yes"]
+    : ["sync", "--strategy", "code", "--source", sourceId];
+
+  const syncResult = spawnSync("gbrain", syncArgs, {
+    stdio: args.quiet ? ["ignore", "ignore", "ignore"] : ["ignore", "inherit", "inherit"],
+    timeout: 35 * 60 * 1000,
+  });
+
+  if (syncResult.status !== 0) {
+    return {
+      name: "code",
+      ran: true,
+      ok: false,
+      duration_ms: Date.now() - t0,
+      summary: `gbrain ${syncArgs.join(" ")} exited ${syncResult.status}`,
+      detail: { source_id: sourceId, source_path: root, status: "failed" },
+    };
+  }
+
+  // Step 3: Read page_count from gbrain sources list.
+  const pageCount = sourcePageCount(sourceId);
+
+  return {
+    name: "code",
+    ran: true,
+    ok: true,
+    duration_ms: Date.now() - t0,
+    summary: `${registered ? "registered + " : ""}synced ${sourceId} (page_count=${pageCount ?? "unknown"})`,
+    detail: {
+      source_id: sourceId,
+      source_path: root,
+      page_count: pageCount,
+      last_imported: new Date().toISOString(),
+      status: "ok",
+    },
+  };
+}
+
+/**
+ * Synchronous mirror of ensureSourceRegistered for use inside the synchronous
+ * stage runner. Returns true if registration changed (added or re-added).
+ */
+function ensureSourceRegisteredSync(id: string, path: string): boolean {
+  // Probe.
+  let probeOut: string;
+  try {
+    probeOut = execFileSync("gbrain", ["sources", "list", "--json"], {
+      encoding: "utf-8",
+      timeout: 10_000,
+      stdio: ["ignore", "pipe", "pipe"],
+    });
+  } catch (err) {
+    const e = err as NodeJS.ErrnoException & { stderr?: Buffer };
+    const stderr = e.stderr?.toString() || "";
+    if (e.code === "ENOENT") throw new Error("gbrain CLI not on PATH");
+    if (stderr.includes("Cannot connect to database") || stderr.includes("config.json")) {
+      throw new Error("gbrain not configured (run /setup-gbrain)");
+    }
+    throw err;
+  }
+
+  let parsed: { sources?: Array<{ id?: string; local_path?: string }> };
+  try {
+    parsed = JSON.parse(probeOut);
+  } catch (err) {
+    throw new Error(`gbrain sources list returned non-JSON: ${(err as Error).message}`);
+  }
+  const sources = parsed.sources || [];
+  const match = sources.find((s) => s.id === id);
+
+  if (match && match.local_path === path) {
+    return false; // no-op
+  }
+
+  if (match && match.local_path !== path) {
+    const rm = spawnSync("gbrain", ["sources", "remove", id, "--yes"], {
+      encoding: "utf-8",
+      timeout: 30_000,
+    });
+    if (rm.status !== 0) {
+      throw new Error(`gbrain sources remove ${id} failed: ${rm.stderr || rm.stdout || `exit ${rm.status}`}`);
+    }
+  }
+
+  const add = spawnSync("gbrain", ["sources", "add", id, "--path", path, "--federated"], {
+    encoding: "utf-8",
+    timeout: 30_000,
+  });
+  if (add.status !== 0) {
+    throw new Error(`gbrain sources add ${id} failed: ${add.stderr || add.stdout || `exit ${add.status}`}`);
+  }
+  return true;
 }
 
 function runMemoryIngest(args: CliArgs): StageResult {
@@ -198,7 +387,7 @@ function runMemoryIngest(args: CliArgs): StageResult {
 
   const result = spawnSync("bun", ingestArgs, {
     encoding: "utf-8",
-    timeout: 35 * 60 * 1000, // honest 35-min ceiling per ED2
+    timeout: 35 * 60 * 1000,
   });
 
   const summary = (result.stderr || "").split("\n").filter((l) => l.includes("[memory-ingest]")).slice(-1)[0] || "ingest pass complete";
@@ -224,7 +413,6 @@ function runBrainSyncPush(args: CliArgs): StageResult {
     return { name: "brain-sync", ran: false, ok: true, duration_ms: 0, summary: "skipped (gstack-brain-sync not installed)" };
   }
 
-  // Discover new artifacts then drain queue
   spawnSync(brainSyncPath, ["--discover-new"], {
     stdio: args.quiet ? ["ignore", "ignore", "ignore"] : ["ignore", "inherit", "inherit"],
     timeout: 60 * 1000,
@@ -243,7 +431,7 @@ function runBrainSyncPush(args: CliArgs): StageResult {
   };
 }
 
-// ── State file (records last sync timestamp + stage outcomes) ──────────────
+// ── State file ─────────────────────────────────────────────────────────────
 
 interface SyncState {
   schema_version: 1;
@@ -266,10 +454,16 @@ function loadSyncState(): SyncState {
   return { schema_version: 1, last_writer: "gstack-gbrain-sync" };
 }
 
+/**
+ * Atomic state file write per /plan-eng-review D1: write tmp file then rename.
+ * rename(2) is atomic on POSIX filesystems.
+ */
 function saveSyncState(state: SyncState): void {
   try {
     mkdirSync(dirname(STATE_PATH), { recursive: true });
-    writeFileSync(STATE_PATH, JSON.stringify(state, null, 2), "utf-8");
+    const tmp = `${STATE_PATH}.tmp.${process.pid}`;
+    writeFileSync(tmp, JSON.stringify(state, null, 2), "utf-8");
+    renameSync(tmp, STATE_PATH);
   } catch {
     // non-fatal
   }
@@ -293,40 +487,67 @@ async function main(): Promise<void> {
     console.error(`[gbrain-sync] mode=${args.mode} engine=${engine.engine}`);
   }
 
-  const state = loadSyncState();
-  const stages: StageResult[] = [];
-
-  if (!args.noCode) {
-    stages.push(await withErrorContext("sync:code", () => runCodeImport(args), "gstack-gbrain-sync"));
-  }
-  if (!args.noMemory) {
-    stages.push(await withErrorContext("sync:memory", () => runMemoryIngest(args), "gstack-gbrain-sync"));
-  }
-  if (!args.noBrainSync) {
-    stages.push(await withErrorContext("sync:brain-sync", () => runBrainSyncPush(args), "gstack-gbrain-sync"));
+  // Acquire lock (skip on dry-run since dry-run never writes).
+  const needsLock = args.mode !== "dry-run";
+  let haveLock = false;
+  if (needsLock) {
+    haveLock = acquireLock();
+    if (!haveLock) {
+      console.error(
+        `[gbrain-sync] another /sync-gbrain is running (lock at ${LOCK_PATH}). ` +
+        `If that process died, the lock auto-clears after 5 min, or remove it manually.`
+      );
+      process.exit(2);
+    }
   }
 
-  // Persist state (skip on dry-run)
-  if (args.mode !== "dry-run") {
-    state.last_sync = new Date().toISOString();
-    if (args.mode === "full") state.last_full_sync = state.last_sync;
-    state.last_stages = stages;
-    saveSyncState(state);
+  const cleanup = () => {
+    if (haveLock) releaseLock();
+  };
+  process.on("SIGINT", () => { cleanup(); process.exit(130); });
+  process.on("SIGTERM", () => { cleanup(); process.exit(143); });
+
+  let exitCode = 0;
+  try {
+    const state = loadSyncState();
+    const stages: StageResult[] = [];
+
+    if (!args.noCode) {
+      stages.push(await withErrorContext("sync:code", () => runCodeImport(args), "gstack-gbrain-sync"));
+    }
+    if (!args.noMemory) {
+      stages.push(await withErrorContext("sync:memory", () => runMemoryIngest(args), "gstack-gbrain-sync"));
+    }
+    if (!args.noBrainSync) {
+      stages.push(await withErrorContext("sync:brain-sync", () => runBrainSyncPush(args), "gstack-gbrain-sync"));
+    }
+
+    if (args.mode !== "dry-run") {
+      state.last_sync = new Date().toISOString();
+      if (args.mode === "full") state.last_full_sync = state.last_sync;
+      state.last_stages = stages;
+      saveSyncState(state);
+    }
+
+    if (!args.quiet || args.mode === "dry-run") {
+      console.log(`\ngstack-gbrain-sync (${args.mode}):`);
+      for (const s of stages) console.log(formatStage(s));
+      const okCount = stages.filter((s) => s.ok).length;
+      const errCount = stages.filter((s) => !s.ok && s.ran).length;
+      console.log(`\n  ${okCount} ok, ${errCount} error, ${stages.length - okCount - errCount} skipped`);
+    }
+
+    const anyError = stages.some((s) => s.ran && !s.ok);
+    exitCode = anyError ? 1 : 0;
+  } finally {
+    cleanup();
   }
 
-  if (!args.quiet || args.mode === "dry-run") {
-    console.log(`\ngstack-gbrain-sync (${args.mode}):`);
-    for (const s of stages) console.log(formatStage(s));
-    const okCount = stages.filter((s) => s.ok).length;
-    const errCount = stages.filter((s) => !s.ok && s.ran).length;
-    console.log(`\n  ${okCount} ok, ${errCount} error, ${stages.length - okCount - errCount} skipped`);
-  }
-
-  const anyError = stages.some((s) => s.ran && !s.ok);
-  process.exit(anyError ? 1 : 0);
+  process.exit(exitCode);
 }
 
 main().catch((err) => {
   console.error(`gstack-gbrain-sync fatal: ${err instanceof Error ? err.message : String(err)}`);
+  releaseLock();
   process.exit(1);
 });
diff --git a/lib/gbrain-sources.ts b/lib/gbrain-sources.ts
new file mode 100644
index 00000000..6cf21955
--- /dev/null
+++ b/lib/gbrain-sources.ts
@@ -0,0 +1,184 @@
+/**
+ * gbrain-sources — TypeScript helper for idempotent gbrain federated source registration.
+ *
+ * Mirrors the bash logic in bin/gstack-gbrain-source-wireup:204-310 but in a form
+ * importable by other TS callers (currently bin/gstack-gbrain-sync.ts; future
+ * callers welcome). gbrain has no `sources update` — drift recovery is
+ * `sources remove` followed by `sources add`.
+ *
+ * Per /plan-eng-review D3 (DRY extraction).
+ */
+
+import { execFileSync, spawnSync } from "child_process";
+import { withErrorContext } from "./gstack-memory-helpers";
+
+export interface SourceState {
+  /** "absent" — id not registered. "match" — id at expected path. "drift" — id at different path. */
+  status: "absent" | "match" | "drift";
+  /** Path gbrain has registered for this id. Only set when status !== "absent". */
+  registered_path?: string;
+}
+
+export interface EnsureResult {
+  /** True if registration state changed (added or re-registered). False on no-op. */
+  changed: boolean;
+  /** Final source state after the call. */
+  state: SourceState;
+}
+
+export interface EnsureOptions {
+  /** Pass --federated to `gbrain sources add`. Default false. */
+  federated?: boolean;
+  /** When status=drift, force a remove+add to update the registered path. Default true. */
+  reregister_on_drift?: boolean;
+  /**
+   * Optional env override for the spawned `gbrain` calls. Production callers
+   * leave this unset (inherit process.env). Tests pass a custom env to point
+   * at a fake `gbrain` on PATH (Bun's execFileSync does not respect runtime
+   * mutations of process.env.PATH unless env is passed explicitly).
+   */
+  env?: NodeJS.ProcessEnv;
+}
+
+/**
+ * Probe the registration state of a source by id.
+ *
+ * Errors:
+ *   - "gbrain CLI not on PATH" (exit 127) — caller should treat as absent + skip stage.
+ *   - "gbrain DB connection failed" — caller should treat as absent + skip stage.
+ *   - JSON parse error — propagate via withErrorContext caller.
+ */
+export function probeSource(id: string, env?: NodeJS.ProcessEnv): SourceState {
+  let stdout: string;
+  try {
+    stdout = execFileSync("gbrain", ["sources", "list", "--json"], {
+      encoding: "utf-8",
+      timeout: 10_000,
+      stdio: ["ignore", "pipe", "pipe"],
+      env,
+    });
+  } catch (err) {
+    const e = err as NodeJS.ErrnoException & { stderr?: Buffer };
+    const stderr = e.stderr?.toString() || "";
+    if (e.code === "ENOENT" || stderr.includes("command not found")) {
+      throw new Error("gbrain CLI not on PATH");
+    }
+    if (stderr.includes("Cannot connect to database") || stderr.includes("config.json")) {
+      throw new Error("gbrain not configured (run /setup-gbrain)");
+    }
+    throw err;
+  }
+
+  let parsed: { sources?: Array<{ id?: string; local_path?: string }> };
+  try {
+    parsed = JSON.parse(stdout);
+  } catch (err) {
+    throw new Error(`gbrain sources list returned non-JSON output: ${(err as Error).message}`);
+  }
+
+  const sources = parsed.sources || [];
+  const match = sources.find((s) => s.id === id);
+  if (!match) return { status: "absent" };
+  return {
+    status: "match",
+    registered_path: match.local_path,
+  };
+}
+
+/**
+ * Ensure source <id> is registered at <path>. Idempotent.
+ *
+ * Behavior:
+ *   - status=absent  → `gbrain sources add <id> --path <path> [--federated]`, returns changed=true.
+ *   - status=match + same path → no-op, returns changed=false.
+ *   - status=match + different path → `sources remove` + `sources add`, returns changed=true.
+ *     (Skip when reregister_on_drift=false; returns changed=false.)
+ *
+ * Caller is responsible for catching errors. The function uses withErrorContext for
+ * forensic logging to ~/.gstack/.gbrain-errors.jsonl.
+ */
+export async function ensureSourceRegistered(
+  id: string,
+  path: string,
+  options: EnsureOptions = {}
+): Promise<EnsureResult> {
+  const federated = options.federated ?? false;
+  const reregister_on_drift = options.reregister_on_drift ?? true;
+  const env = options.env;
+
+  return withErrorContext(`ensureSourceRegistered:${id}`, () => {
+    const probed = probeSource(id, env);
+
+    // Disambiguate match-but-different-path
+    let state: SourceState = probed;
+    if (probed.status === "match" && probed.registered_path !== path) {
+      state = { status: "drift", registered_path: probed.registered_path };
+    }
+
+    if (state.status === "match") {
+      return { changed: false, state };
+    }
+
+    if (state.status === "drift" && !reregister_on_drift) {
+      return { changed: false, state };
+    }
+
+    // For drift, remove first.
+    if (state.status === "drift") {
+      const rm = spawnSync("gbrain", ["sources", "remove", id, "--yes"], {
+        encoding: "utf-8",
+        timeout: 30_000,
+        env,
+      });
+      if (rm.status !== 0) {
+        throw new Error(`gbrain sources remove ${id} failed: ${rm.stderr || rm.stdout || `exit ${rm.status}`}`);
+      }
+    }
+
+    // Add.
+    const addArgs = ["sources", "add", id, "--path", path];
+    if (federated) addArgs.push("--federated");
+    const add = spawnSync("gbrain", addArgs, {
+      encoding: "utf-8",
+      timeout: 30_000,
+      env,
+    });
+    if (add.status !== 0) {
+      throw new Error(`gbrain sources add ${id} failed: ${add.stderr || add.stdout || `exit ${add.status}`}`);
+    }
+
+    return {
+      changed: true,
+      state: { status: "match", registered_path: path },
+    };
+  }, "gbrain-sources");
+}
+
+/**
+ * Get page_count for a registered source. Returns null if source is absent or if
+ * page_count is missing/invalid in the JSON. Used by the verdict block + preamble
+ * variant selection.
+ */
+export function sourcePageCount(id: string, env?: NodeJS.ProcessEnv): number | null {
+  let stdout: string;
+  try {
+    stdout = execFileSync("gbrain", ["sources", "list", "--json"], {
+      encoding: "utf-8",
+      timeout: 10_000,
+      stdio: ["ignore", "pipe", "pipe"],
+      env,
+    });
+  } catch {
+    return null;
+  }
+
+  try {
+    const parsed = JSON.parse(stdout) as { sources?: Array<{ id?: string; page_count?: number }> };
+    const match = (parsed.sources || []).find((s) => s.id === id);
+    if (!match) return null;
+    if (typeof match.page_count !== "number") return null;
+    return match.page_count;
+  } catch {
+    return null;
+  }
+}
diff --git a/test/gbrain-sources.test.ts b/test/gbrain-sources.test.ts
new file mode 100644
index 00000000..9486eb06
--- /dev/null
+++ b/test/gbrain-sources.test.ts
@@ -0,0 +1,219 @@
+/**
+ * Unit tests for lib/gbrain-sources.ts (per /plan-eng-review D3 DRY extraction).
+ *
+ * The helper shells out to the real `gbrain` CLI. To test idempotency
+ * deterministically without a live brain, we put a fake `gbrain` binary on
+ * PATH that emits canned `sources list --json` output and records its
+ * invocations. The same trick `test/gstack-gbrain-source-wireup.test.ts` uses.
+ */
+
+import { describe, it, expect } from "bun:test";
+import { mkdtempSync, writeFileSync, readFileSync, existsSync, mkdirSync, rmSync, chmodSync } from "fs";
+import { tmpdir } from "os";
+import { join } from "path";
+
+import { ensureSourceRegistered, probeSource, sourcePageCount } from "../lib/gbrain-sources";
+
+interface FakeGbrainSetup {
+  bindir: string;
+  statePath: string;
+  logPath: string;
+  /**
+   * Env to pass to helper calls. Bun's execFileSync does NOT respect runtime
+   * mutations of process.env.PATH; we have to pass env explicitly. Production
+   * callers leave this unset (inherit process.env) — the helper signature has
+   * an optional `env` param specifically for tests.
+   */
+  env: NodeJS.ProcessEnv;
+  cleanup: () => void;
+}
+
+/**
+ * Build a temp dir with a fake `gbrain` shell script on PATH. The fake honors:
+ *   gbrain sources list --json     → cat $STATE_PATH
+ *   gbrain sources add <id> --path <p> [--federated]  → append to state, log
+ *   gbrain sources remove <id> --yes                  → drop from state, log
+ *   gbrain --version                                  → echo "gbrain 0.25.1"
+ * Anything else exits 1.
+ */
+function makeFakeGbrain(initialState: { sources: Array<{ id: string; local_path: string; federated?: boolean; page_count?: number }> }): FakeGbrainSetup {
+  const tmp = mkdtempSync(join(tmpdir(), "gbrain-sources-test-"));
+  const bindir = join(tmp, "bin");
+  mkdirSync(bindir, { recursive: true });
+  const statePath = join(tmp, "state.json");
+  const logPath = join(tmp, "calls.log");
+  writeFileSync(statePath, JSON.stringify(initialState));
+  writeFileSync(logPath, "");
+
+  const fake = `#!/bin/sh
+echo "$@" >> "${logPath}"
+case "$1 $2" in
+  "--version ")
+    echo "gbrain 0.25.1"
+    exit 0
+    ;;
+  "sources list")
+    cat "${statePath}"
+    exit 0
+    ;;
+  "sources add")
+    ID="$3"
+    shift 3
+    PATH_VAL=""
+    FED="false"
+    while [ $# -gt 0 ]; do
+      case "$1" in
+        --path) PATH_VAL="$2"; shift 2 ;;
+        --federated) FED="true"; shift ;;
+        *) shift ;;
+      esac
+    done
+    NEW=$(jq --arg id "$ID" --arg path "$PATH_VAL" --argjson fed "$FED" \
+      '.sources += [{id: $id, local_path: $path, federated: $fed, page_count: 0}]' "${statePath}")
+    echo "$NEW" > "${statePath}"
+    exit 0
+    ;;
+  "sources remove")
+    ID="$3"
+    NEW=$(jq --arg id "$ID" '.sources = (.sources | map(select(.id != $id)))' "${statePath}")
+    echo "$NEW" > "${statePath}"
+    exit 0
+    ;;
+esac
+echo "fake gbrain: unknown command: $@" >&2
+exit 1
+`;
+  const fakePath = join(bindir, "gbrain");
+  writeFileSync(fakePath, fake);
+  chmodSync(fakePath, 0o755);
+
+  // Build the env override we'll pass to helper calls. We do NOT mutate
+  // process.env globally because Bun's execFileSync caches PATH at process
+  // start; explicit env is the only reliable way to redirect spawn-time PATH.
+  const env: NodeJS.ProcessEnv = { ...process.env, PATH: `${bindir}:${process.env.PATH || ""}` };
+
+  return {
+    bindir,
+    statePath,
+    logPath,
+    env,
+    cleanup: () => {
+      rmSync(tmp, { recursive: true, force: true });
+    },
+  };
+}
+
+describe("probeSource", () => {
+  it("returns absent when source id is not in the list", () => {
+    const fake = makeFakeGbrain({ sources: [{ id: "other-source", local_path: "/x" }] });
+    const state = probeSource("gstack-code-foo", fake.env);
+    expect(state.status).toBe("absent");
+    expect(state.registered_path).toBeUndefined();
+    fake.cleanup();
+  });
+
+  it("returns match when source id is registered (path included)", () => {
+    const fake = makeFakeGbrain({
+      sources: [{ id: "gstack-code-foo", local_path: "/Users/me/repo" }],
+    });
+    const state = probeSource("gstack-code-foo", fake.env);
+    expect(state.status).toBe("match");
+    expect(state.registered_path).toBe("/Users/me/repo");
+    fake.cleanup();
+  });
+});
+
+describe("ensureSourceRegistered", () => {
+  it("adds source when absent, returns changed=true", async () => {
+    const fake = makeFakeGbrain({ sources: [] });
+    const result = await ensureSourceRegistered("gstack-code-foo", "/Users/me/repo", {
+      federated: true,
+      env: fake.env,
+    });
+    expect(result.changed).toBe(true);
+    expect(result.state.status).toBe("match");
+    expect(result.state.registered_path).toBe("/Users/me/repo");
+
+    const log = readFileSync(fake.logPath, "utf-8");
+    expect(log).toContain("sources add gstack-code-foo --path /Users/me/repo --federated");
+    expect(log).not.toContain("sources remove");
+    fake.cleanup();
+  });
+
+  it("is a no-op when source is already at the correct path, returns changed=false", async () => {
+    const fake = makeFakeGbrain({
+      sources: [{ id: "gstack-code-foo", local_path: "/Users/me/repo" }],
+    });
+    const result = await ensureSourceRegistered("gstack-code-foo", "/Users/me/repo", { env: fake.env });
+    expect(result.changed).toBe(false);
+    expect(result.state.status).toBe("match");
+
+    const log = readFileSync(fake.logPath, "utf-8");
+    expect(log).toContain("sources list --json");
+    expect(log).not.toContain("sources add");
+    expect(log).not.toContain("sources remove");
+    fake.cleanup();
+  });
+
+  it("recreates source when path differs (gbrain has no `sources update`), returns changed=true", async () => {
+    const fake = makeFakeGbrain({
+      sources: [{ id: "gstack-code-foo", local_path: "/old/path" }],
+    });
+    const result = await ensureSourceRegistered("gstack-code-foo", "/new/path", {
+      federated: true,
+      env: fake.env,
+    });
+    expect(result.changed).toBe(true);
+    expect(result.state.status).toBe("match");
+    expect(result.state.registered_path).toBe("/new/path");
+
+    const log = readFileSync(fake.logPath, "utf-8");
+    expect(log).toContain("sources remove gstack-code-foo --yes");
+    expect(log).toContain("sources add gstack-code-foo --path /new/path --federated");
+    fake.cleanup();
+  });
+
+  it("when reregister_on_drift=false and source is at different path, returns changed=false", async () => {
+    const fake = makeFakeGbrain({
+      sources: [{ id: "gstack-code-foo", local_path: "/old/path" }],
+    });
+    const result = await ensureSourceRegistered("gstack-code-foo", "/new/path", {
+      reregister_on_drift: false,
+      env: fake.env,
+    });
+    expect(result.changed).toBe(false);
+    expect(result.state.status).toBe("drift");
+    expect(result.state.registered_path).toBe("/old/path");
+
+    const log = readFileSync(fake.logPath, "utf-8");
+    expect(log).not.toContain("sources remove");
+    expect(log).not.toContain("sources add");
+    fake.cleanup();
+  });
+});
+
+describe("sourcePageCount", () => {
+  it("returns the page_count when the source is registered", () => {
+    const fake = makeFakeGbrain({
+      sources: [
+        { id: "gstack-code-foo", local_path: "/x", page_count: 1247 },
+        { id: "other-source", local_path: "/y", page_count: 99 },
+      ],
+    });
+    expect(sourcePageCount("gstack-code-foo", fake.env)).toBe(1247);
+    expect(sourcePageCount("other-source", fake.env)).toBe(99);
+    fake.cleanup();
+  });
+
+  it("returns null when the source is absent", () => {
+    const fake = makeFakeGbrain({ sources: [{ id: "other", local_path: "/x", page_count: 5 }] });
+    expect(sourcePageCount("missing", fake.env)).toBeNull();
+    fake.cleanup();
+  });
+
+  it("returns null when page_count is missing from the source object", () => {
+    const fake = makeFakeGbrain({ sources: [{ id: "no-count", local_path: "/x" } as { id: string; local_path: string }] });
+    expect(sourcePageCount("no-count", fake.env)).toBeNull();
+    fake.cleanup();
+  });
+});
diff --git a/test/gstack-gbrain-sync.test.ts b/test/gstack-gbrain-sync.test.ts
index c8841268..100d2e27 100644
--- a/test/gstack-gbrain-sync.test.ts
+++ b/test/gstack-gbrain-sync.test.ts
@@ -55,7 +55,11 @@ describe("gstack-gbrain-sync CLI", () => {
 
     const r = runScript(["--dry-run", "--code-only", "--quiet"], { HOME: home, GSTACK_HOME: gstackHome });
     expect(r.exitCode).toBe(0);
-    expect(r.stdout).toContain("would: gbrain import");
+    // Code stage now uses native code surface: sources add + sync --strategy code
+    // (NOT gbrain import — that's the markdown-only path that was rejected post-codex).
+    expect(r.stdout).toContain("would: gbrain sources add");
+    expect(r.stdout).toContain("gbrain sync --strategy code");
+    expect(r.stdout).not.toContain("gbrain import");
     // memory + brain-sync stages should not appear
     expect(r.stdout).not.toContain("gstack-memory-ingest --probe");
     expect(r.stdout).not.toContain("gstack-brain-sync --discover-new");
@@ -69,7 +73,8 @@ describe("gstack-gbrain-sync CLI", () => {
 
     const r = runScript(["--dry-run"], { HOME: home, GSTACK_HOME: gstackHome });
     expect(r.exitCode).toBe(0);
-    expect(r.stdout).toContain("would: gbrain import");
+    expect(r.stdout).toContain("would: gbrain sources add");
+    expect(r.stdout).toContain("gbrain sync --strategy code");
     expect(r.stdout).toContain("would: gstack-memory-ingest");
     expect(r.stdout).toContain("would: gstack-brain-sync");
     rmSync(home, { recursive: true, force: true });
@@ -82,11 +87,84 @@ describe("gstack-gbrain-sync CLI", () => {
 
     const r = runScript(["--dry-run", "--no-code"], { HOME: home, GSTACK_HOME: gstackHome });
     expect(r.exitCode).toBe(0);
-    expect(r.stdout).not.toContain("would: gbrain import");
+    expect(r.stdout).not.toContain("would: gbrain sources add");
     expect(r.stdout).toContain("would: gstack-memory-ingest");
     rmSync(home, { recursive: true, force: true });
   });
 
+  it("dry-run derives a stable source id from the canonical git remote", () => {
+    // The source id pattern is `gstack-code-<canonicalized-remote>`. For this
+    // repo (github.com/garrytan/gstack), the slug should appear in the dry-run
+    // preview line. We don't pin the exact slug — just verify the prefix +
+    // that the preview command would target a source with id gstack-code-*.
+    const home = makeTestHome();
+    const gstackHome = join(home, ".gstack");
+    mkdirSync(gstackHome, { recursive: true });
+
+    const r = runScript(["--dry-run", "--code-only", "--quiet"], { HOME: home, GSTACK_HOME: gstackHome });
+    expect(r.exitCode).toBe(0);
+    expect(r.stdout).toMatch(/gbrain sources add gstack-code-[a-z0-9-]+/);
+    expect(r.stdout).toMatch(/gbrain sync --strategy code --source gstack-code-[a-z0-9-]+/);
+    rmSync(home, { recursive: true, force: true });
+  });
+
+  it("dry-run does NOT acquire the lock file (lock is for write paths only)", () => {
+    const home = makeTestHome();
+    const gstackHome = join(home, ".gstack");
+    mkdirSync(gstackHome, { recursive: true });
+
+    const r = runScript(["--dry-run"], { HOME: home, GSTACK_HOME: gstackHome });
+    expect(r.exitCode).toBe(0);
+    // Lock file should not exist after a dry-run (it's a write-only safety primitive).
+    const lockPath = join(gstackHome, ".sync-gbrain.lock");
+    expect(existsSync(lockPath)).toBe(false);
+    rmSync(home, { recursive: true, force: true });
+  });
+
+  it("a stale lock file (older than 5 min) is taken over, not blocking", () => {
+    const home = makeTestHome();
+    const gstackHome = join(home, ".gstack");
+    mkdirSync(gstackHome, { recursive: true });
+
+    // Plant a stale lock file (mtime 6 min ago).
+    const lockPath = join(gstackHome, ".sync-gbrain.lock");
+    writeFileSync(lockPath, JSON.stringify({ pid: 99999, started_at: new Date(Date.now() - 6 * 60 * 1000).toISOString() }));
+    const sixMinAgo = (Date.now() - 6 * 60 * 1000) / 1000;
+    // Set mtime explicitly via Bun's fs.utimes
+    const fs = require("fs");
+    fs.utimesSync(lockPath, sixMinAgo, sixMinAgo);
+
+    // Run with all stages disabled so we don't actually invoke anything heavy.
+    const r = runScript(["--incremental", "--no-code", "--no-memory", "--no-brain-sync", "--quiet"], {
+      HOME: home,
+      GSTACK_HOME: gstackHome,
+    });
+    expect(r.exitCode).toBe(0);
+    // Lock should be cleared after the run (we took it over and released).
+    expect(existsSync(lockPath)).toBe(false);
+    rmSync(home, { recursive: true, force: true });
+  });
+
+  it("a fresh lock file (less than 5 min old) blocks a second invocation with exit 2", () => {
+    const home = makeTestHome();
+    const gstackHome = join(home, ".gstack");
+    mkdirSync(gstackHome, { recursive: true });
+
+    // Plant a fresh lock file (mtime now).
+    const lockPath = join(gstackHome, ".sync-gbrain.lock");
+    writeFileSync(lockPath, JSON.stringify({ pid: 99999, started_at: new Date().toISOString() }));
+
+    const r = runScript(["--incremental", "--no-code", "--no-memory", "--no-brain-sync", "--quiet"], {
+      HOME: home,
+      GSTACK_HOME: gstackHome,
+    });
+    expect(r.exitCode).toBe(2);
+    expect(r.stderr).toContain("another /sync-gbrain is running");
+    // Lock should still be there — the second invocation didn't take it over.
+    expect(existsSync(lockPath)).toBe(true);
+    rmSync(home, { recursive: true, force: true });
+  });
+
   it("writes a state file with schema_version: 1 after a non-dry run", () => {
     const home = makeTestHome();
     const gstackHome = join(home, ".gstack");
diff --git a/test/skill-e2e-memory-pipeline.test.ts b/test/skill-e2e-memory-pipeline.test.ts
index c919315c..c0f40f61 100644
--- a/test/skill-e2e-memory-pipeline.test.ts
+++ b/test/skill-e2e-memory-pipeline.test.ts
@@ -183,7 +183,10 @@ describe("V1 /gbrain-sync orchestrator E2E", () => {
 
     const r = runBun(SYNC, ["--dry-run"], env);
     expect(r.exitCode).toBe(0);
-    expect(r.stdout).toContain("would: gbrain import");
+    // Code stage uses native gbrain code surfaces (sources add + sync --strategy code)
+    // post-codex review; NOT `gbrain import` (markdown-only path).
+    expect(r.stdout).toContain("would: gbrain sources add");
+    expect(r.stdout).toContain("gbrain sync --strategy code");
     expect(r.stdout).toContain("would: gstack-memory-ingest");
     expect(r.stdout).toContain("would: gstack-brain-sync");