diff --git a/claims.json b/claims.json
index f601fdb..d54a3d4 100644
--- a/claims.json
+++ b/claims.json
@@ -14,8 +14,8 @@
     "networkMillis": 300
   },
   "tests": {
-    "count": 1503,
-    "assertions": 7211,
-    "files": 235
+    "count": 1505,
+    "assertions": 7218,
+    "files": 236
   }
 }
diff --git a/src/cli/branch.ts b/src/cli/branch.ts
new file mode 100644
index 0000000..c98fd1a
--- /dev/null
+++ b/src/cli/branch.ts
@@ -0,0 +1,56 @@
+import { requireRoot, usageError } from "./shared.ts";
+import type { ParsedArgs } from "./shared.ts";
+import {
+  createBranchOverlay,
+  currentGitBranch,
+  dropBranchOverlay,
+  listBranchMemories,
+  loadBranchOverlay,
+  mergeBranchOverlay,
+} from "../store/branch.ts";
+
+export async function handleBranchCommand({ positional, flags }: ParsedArgs): Promise<number> {
+  const ctx = requireRoot(flags);
+  if (!ctx) return 1;
+  const sub = positional[0] ?? "show";
+  const branch = positional[1] ?? flags["branch"] ?? currentGitBranch(ctx.root) ?? undefined;
+  if (!branch && sub !== "list") return usageError("branch requires a branch name or a git checkout");
+
+  switch (sub) {
+    case "list": {
+      const branchName = currentGitBranch(ctx.root);
+      const overlay = branchName ? loadBranchOverlay(ctx.memoryDir, branchName) : null;
+      console.log(branchName ?? "(detached)");
+      if (overlay) console.log(`overlay: ${overlay.entries.length} entry(ies), ${overlay.deleted_ids.length} deletion(s)`);
+      return 0;
+    }
+    case "create": {
+      const overlay = createBranchOverlay(ctx.store, { branch, baseBranch: flags["base"] });
+      console.log(`branch overlay ready: ${overlay.meta.branch}`);
+      return 0;
+    }
+    case "show": {
+      const overlay = loadBranchOverlay(ctx.memoryDir, branch!);
+      if (!overlay) return usageError(`no overlay for '${branch}'`);
+      console.log(`${overlay.meta.branch} (base ${overlay.meta.base_branch ?? "?"})`);
+      for (const entry of overlay.entries) console.log(`  ${entry.id} ${entry.status} ${entry.title}`);
+      return 0;
+    }
+    case "merge": {
+      const report = mergeBranchOverlay(ctx.store, branch!);
+      console.log(`merged ${report.branch}: ${report.applied.length} applied, ${report.deleted.length} archived`);
+      return 0;
+    }
+    case "drop": {
+      if (!dropBranchOverlay(ctx.store, branch!)) return usageError(`no overlay for '${branch}'`);
+      console.log(`dropped ${branch}`);
+      return 0;
+    }
+    case "entries": {
+      for (const entry of listBranchMemories(ctx.store, branch!)) console.log(`${entry.id} ${entry.status} ${entry.title}`);
+      return 0;
+    }
+    default:
+      return usageError(`unknown branch subcommand '${sub}' (expected list | create | show | entries | merge | drop)`);
+  }
+}
diff --git a/src/store/branch.ts b/src/store/branch.ts
new file mode 100644
index 0000000..6c5c139
--- /dev/null
+++ b/src/store/branch.ts
@@ -0,0 +1,149 @@
+import { existsSync, mkdirSync, readFileSync, renameSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+import { execFileSync } from "node:child_process";
+import type { Store } from "../store.ts";
+import { list, get, save } from "../store.ts";
+import type { MemoryEntry } from "../types.ts";
+
+export interface BranchOverlayMeta {
+  branch: string;
+  base_branch?: string;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface BranchOverlay {
+  meta: BranchOverlayMeta;
+  entries: MemoryEntry[];
+  deleted_ids: string[];
+}
+
+function safeName(branch: string): string {
+  return branch.replace(/[^A-Za-z0-9._-]/g, "_");
+}
+
+export function branchOverlayPath(memoryDir: string, branch: string): string {
+  return join(memoryDir, "branches", `${safeName(branch)}.json`);
+}
+
+export function currentGitBranch(cwd: string = process.cwd()): string | null {
+  try {
+    return execFileSync("git", ["rev-parse", "--abbrev-ref", "HEAD"], {
+      cwd,
+      encoding: "utf8",
+      stdio: ["ignore", "pipe", "ignore"],
+    }).trim() || null;
+  } catch {
+    return null;
+  }
+}
+
+export function loadBranchOverlay(memoryDir: string, branch: string): BranchOverlay | null {
+  const path = branchOverlayPath(memoryDir, branch);
+  if (!existsSync(path)) return null;
+  const parsed = JSON.parse(readFileSync(path, "utf8")) as Partial<BranchOverlay>;
+  if (!parsed || typeof parsed !== "object" || !Array.isArray(parsed.entries)) {
+    throw new Error(`Invalid branch overlay at ${path}`);
+  }
+  return {
+    meta: {
+      branch: parsed.meta?.branch ?? branch,
+      base_branch: parsed.meta?.base_branch,
+      created_at: parsed.meta?.created_at ?? new Date().toISOString(),
+      updated_at: parsed.meta?.updated_at ?? new Date().toISOString(),
+    },
+    entries: parsed.entries as MemoryEntry[],
+    deleted_ids: Array.isArray(parsed.deleted_ids) ? parsed.deleted_ids : [],
+  };
+}
+
+function writeOverlay(memoryDir: string, overlay: BranchOverlay): void {
+  const dir = join(memoryDir, "branches");
+  mkdirSync(dir, { recursive: true });
+  const path = branchOverlayPath(memoryDir, overlay.meta.branch);
+  const tmp = `${path}.${process.pid}.tmp`;
+  writeFileSync(tmp, JSON.stringify(overlay, null, 2) + "\n", "utf8");
+  renameSync(tmp, path);
+}
+
+export function createBranchOverlay(
+  store: Store,
+  options: { branch?: string; baseBranch?: string } = {},
+): BranchOverlay {
+  const branch = options.branch ?? currentGitBranch(store.dir);
+  if (!branch) throw new Error("Cannot determine branch: pass --branch");
+  const existing = loadBranchOverlay(store.memoryDir ?? store.dir, branch);
+  if (existing) return existing;
+  const now = new Date().toISOString();
+  const overlay: BranchOverlay = {
+    meta: { branch, base_branch: options.baseBranch, created_at: now, updated_at: now },
+    entries: [],
+    deleted_ids: [],
+  };
+  writeOverlay(store.memoryDir ?? store.dir, overlay);
+  return overlay;
+}
+
+/** Base store plus branch overlay, with overlay entries winning by id. */
+export function listBranchMemories(store: Store, branch: string): MemoryEntry[] {
+  const overlay = loadBranchOverlay(store.memoryDir ?? store.dir, branch);
+  if (!overlay) return list(store);
+  const deleted = new Set(overlay.deleted_ids);
+  const byId = new Map(list(store).filter((entry) => !deleted.has(entry.id)).map((entry) => [entry.id, entry]));
+  for (const entry of overlay.entries) byId.set(entry.id, entry);
+  return [...byId.values()];
+}
+
+export function writeBranchEntry(store: Store, branch: string, entry: MemoryEntry): BranchOverlay {
+  const memoryDir = store.memoryDir ?? store.dir;
+  const overlay = loadBranchOverlay(memoryDir, branch) ?? createBranchOverlay(store, { branch });
+  overlay.entries = overlay.entries.filter((candidate) => candidate.id !== entry.id);
+  overlay.entries.push(entry);
+  overlay.deleted_ids = overlay.deleted_ids.filter((id) => id !== entry.id);
+  overlay.meta.updated_at = new Date().toISOString();
+  writeOverlay(memoryDir, overlay);
+  return overlay;
+}
+
+export function deleteBranchEntry(store: Store, branch: string, id: string): BranchOverlay {
+  const memoryDir = store.memoryDir ?? store.dir;
+  const overlay = loadBranchOverlay(memoryDir, branch) ?? createBranchOverlay(store, { branch });
+  overlay.entries = overlay.entries.filter((entry) => entry.id !== id);
+  if (!overlay.deleted_ids.includes(id)) overlay.deleted_ids.push(id);
+  overlay.meta.updated_at = new Date().toISOString();
+  writeOverlay(memoryDir, overlay);
+  return overlay;
+}
+
+export interface MergeReport {
+  branch: string;
+  applied: string[];
+  deleted: string[];
+}
+
+/** Apply an overlay to the base store and clear it. */
+export function mergeBranchOverlay(store: Store, branch: string): MergeReport {
+  const memoryDir = store.memoryDir ?? store.dir;
+  const overlay = loadBranchOverlay(memoryDir, branch);
+  if (!overlay) return { branch, applied: [], deleted: [] };
+  const applied: string[] = [];
+  for (const entry of overlay.entries) {
+    const current = get(store, entry.id);
+    save(store, current ? { ...current, ...entry } : entry);
+    applied.push(entry.id);
+  }
+  for (const id of overlay.deleted_ids) {
+    const current = get(store, id);
+    if (current) save(store, { ...current, status: "archived" });
+  }
+  const path = branchOverlayPath(memoryDir, branch);
+  if (existsSync(path)) renameSync(path, `${path}.merged`);
+  return { branch, applied, deleted: overlay.deleted_ids };
+}
+
+export function dropBranchOverlay(store: Store, branch: string): boolean {
+  const path = branchOverlayPath(store.memoryDir ?? store.dir, branch);
+  if (!existsSync(path)) return false;
+  renameSync(path, `${path}.dropped`);
+  return true;
+}
diff --git a/test/branch_overlays.test.ts b/test/branch_overlays.test.ts
new file mode 100644
index 0000000..e476496
--- /dev/null
+++ b/test/branch_overlays.test.ts
@@ -0,0 +1,53 @@
+import { describe, test, expect } from "bun:test";
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { openStore, propose, list, get } from "../src/store.ts";
+import {
+  createBranchOverlay,
+  writeBranchEntry,
+  listBranchMemories,
+  mergeBranchOverlay,
+  dropBranchOverlay,
+  loadBranchOverlay,
+} from "../src/store/branch.ts";
+
+describe("T-436: branchable memory overlays", () => {
+  test("isolates branch writes from the base store and merges them back", () => {
+    const memoryDir = mkdtempSync(join(tmpdir(), "muse-branch-"));
+    try {
+      const store = openStore(memoryDir);
+      const base = propose(store, { content: "base rule", project: "p", type: "constraint", confirmed: true });
+      createBranchOverlay(store, { branch: "feat/x", baseBranch: "dev" });
+      const overlayEntry = {
+        ...base,
+        id: "m_9999999999999_overlayrule",
+        content: "overlay rule",
+        title: "overlay rule",
+      };
+      writeBranchEntry(store, "feat/x", overlayEntry);
+
+      expect(list(store).map((entry) => entry.id)).toEqual([base.id]);
+      expect(listBranchMemories(store, "feat/x").map((entry) => entry.id).sort()).toEqual([base.id, overlayEntry.id].sort());
+
+      const report = mergeBranchOverlay(store, "feat/x");
+      expect(report.applied).toEqual([overlayEntry.id]);
+      expect(get(store, overlayEntry.id)?.content).toBe("overlay rule");
+      expect(loadBranchOverlay(memoryDir, "feat/x")).toBeNull();
+    } finally {
+      rmSync(memoryDir, { recursive: true, force: true });
+    }
+  });
+
+  test("drops an overlay without touching the base store", () => {
+    const memoryDir = mkdtempSync(join(tmpdir(), "muse-branch-drop-"));
+    try {
+      const store = openStore(memoryDir);
+      createBranchOverlay(store, { branch: "feat/y" });
+      expect(dropBranchOverlay(store, "feat/y")).toBe(true);
+      expect(loadBranchOverlay(memoryDir, "feat/y")).toBeNull();
+    } finally {
+      rmSync(memoryDir, { recursive: true, force: true });
+    }
+  });
+});