diff --git a/Makefile b/Makefile
index 7d29268..33ab6d0 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-.PHONY: bootstrap setup install test lint fmt fmt-check check docker hooks build clean dev
+.PHONY: bootstrap setup install test lint fmt fmt-check check docker hooks build build-debug clean dev
 
 # Standard targets are thin shims; the implementations live in script/
 # per the scripts-to-rule-them-all pattern (see the Entrypoints section
@@ -38,6 +38,13 @@ build:
 	@echo "Building extension..."
 	@yarn run build 2>&1
 
+# Development-only build: enables the red DEBUG / INSECURE banner and makes
+# the hardcoded test recovery phrase the output of wallet creation. Never
+# distribute the artifacts this produces.
+build-debug:
+	@echo "Building extension (DEBUG)..."
+	@AUTISTMASK_DEBUG=1 yarn run build 2>&1
+
 clean:
 	@rm -rf dist/
 
diff --git a/README.md b/README.md
index 618e757..a4023da 100644
--- a/README.md
+++ b/README.md
@@ -42,6 +42,23 @@ Load the extension:
 - **Firefox**: Navigate to `about:debugging#/runtime/this-firefox`, click "Load
   Temporary Add-on", and select `dist/firefox/manifest.json`.
 
+### Debug Builds
+
+`make build` always produces a release build: the build-time `DEBUG` constant is
+`false`, so wallet creation uses real entropy and the red banner is off. To
+produce a debug build instead, set `AUTISTMASK_DEBUG=1` in the environment:
+
+```bash
+make build-debug          # or: AUTISTMASK_DEBUG=1 make build
+```
+
+Only the exact value `1` enables it; any other value (including unset, empty, or
+`true`) yields a release build, so a typo cannot accidentally ship the debug
+behavior. The build prints which mode it used. See the
+[DEBUG Mode Policy](#debug-mode-policy) for what the flag changes. **Never
+distribute a debug build** — every wallet it creates gets the same publicly
+known test recovery phrase.
+
 ## Entrypoints
 
 This repository adheres to the
@@ -668,6 +685,19 @@ flows, or alter program behavior beyond the banner and the hardcoded mnemonic.
 Adding new DEBUG-conditional branches requires explicit approval from the
 project owner.
 
+`DEBUG` is a build-time constant, not a runtime setting. `build.js` injects it
+into the bundle as the `__BUILD_DEBUG__` define — `false` unless the build was
+run with `AUTISTMASK_DEBUG=1` (see [Debug Builds](#debug-builds)) — and
+`src/shared/constants.js` reads it. It cannot be changed after the bundle is
+produced.
+
+The debug-mode toggle in settings is a separate, runtime-only flag. It raises
+the log level and turns the banner on, and that is all it may ever do: it feeds
+`isDebug()` in `src/shared/log.js`, which is deliberately not what
+`generateMnemonic()` consults. Mnemonic generation reads the build-time `DEBUG`
+constant directly, so no runtime toggle in a release build can reach the
+hardcoded test phrase.
+
 ### Key Decisions
 
 - **No framework**: The popup UI is vanilla JS and HTML. The extension is small
diff --git a/TODO.md b/TODO.md
index 5677a1b..b94902f 100644
--- a/TODO.md
+++ b/TODO.md
@@ -10,24 +10,31 @@
 
 # Status
 
-pre-1.0. Tagged v0.1.0 on 2026-02-27. Active development on branch
-feat/issue-144-settings-about (another agent working as of 2026-07-06). Full
-policy file set present; make check on main not verified.
+pre-1.0, working towards the 1.0.0 milestone. Tagged v0.1.0 on 2026-02-27. No
+other branch is in flight: the settings About well landed as #145 on 2026-07-26
+and scripts-to-rule-them-all landed as #148, so the `scripts/` directory
+question is resolved. Full policy file set present. `make check` verified
+passing on `main` at `23aeae4` on 2026-08-09. The 1.0.0 backlog is filed as
+#149-#168.
 
 # Next Step
 
-Land feat/issue-144-settings-about: finish the settings About well (build info,
-app name and repo link, release date, version click easter egg, git info derived
-inside Docker), resolve the untracked scripts/ directory (commit or gitignore),
-get review, merge to main.
+Land #149: make `DEBUG` a build-time constant that defaults to off, injected as
+the `__BUILD_DEBUG__` esbuild define from `AUTISTMASK_DEBUG=1`, so a plain
+`make build` stops handing every newly created wallet the publicly committed
+test recovery phrase. Branch `fix/issue-149-debug-build-flag`; PR open, awaiting
+review.
 
 # Completed Steps
 
+- 2026-08-09: Reviewed the repo end to end and filed the 1.0.0 backlog
+  (#149-#168).
+- 2026-07-26: About well in settings with build info, repo link and the version
+  click easter egg (#145); proper view navigation stack (#146).
 - 2026-07-07 Adopted scripts-to-rule-them-all: `script/` entrypoints, Makefile
-  shims, README Entrypoints section
-- 2026-03-01: About well in settings with build info and easter egg (in flight
-  on feature branch); USD display suppressed on testnets (#142); estimated USD
-  for ETH in approve-tx view (#141).
+  shims, README Entrypoints section (#148)
+- 2026-03-01: USD display suppressed on testnets (#142); estimated USD for ETH
+  in approve-tx view (#141).
 - Sepolia testnet support (#137); etherscan links go to token-specific URLs
   (#136).
 - Transaction detail improvements: Type field and on-chain details (#130),
@@ -45,12 +52,32 @@ get review, merge to main.
 
 # Future Steps
 
-- Verify main passes make check after the feature branch merges (not verified
-  2026-07-06 because an agent was active in the tree); fix anything red. main
-  must always be green.
-- Prune stale branches: dozens of merged local and remote feature branches
-  remain (fix/_, feature/_, tx-\*); delete merged ones locally and on origin.
-- Continue the issue backlog toward a feature-complete wallet, then cut further
-  tags as milestones land.
+- Fix the two `ReferenceError` crashes that make whole screens unreachable:
+  AddToken (#150) and TransactionDetail for every ERC-20 transfer (#151).
+- Add ESLint to `script/lint` (#152). `make check` is `prettier --check` only
+  and cannot catch undefined identifiers, which is how #150 and #151 shipped.
+- Make the Firefox target functional: Chrome callback APIs are used against the
+  promise-only `browser` namespace (#153).
+- Send and transaction-flow correctness: gas fee excluded from the
+  insufficient-balance check (#154), WaitTx 60s timeout overwriting a rendered
+  success screen (#155), last-wallet deletion leaving inconsistent state (#156).
+- Security: plaintext password crossing the extension messaging boundary during
+  dApp approvals (#157); MV3 service worker termination killing the background
+  refresh and the 24h phishing list update (#158).
+- Test the crypto core — `wallet.js` derivation and `vault.js` encryption (#159)
+  — and the address-poisoning defense in `transactions.js` (#160).
+- Wallet features for 1.0: show a wallet's recovery phrase behind the password
+  (#161), delete an address from an HD wallet (#162).
+- Docs: `docs/README.md` contradicts the code on external services and names
+  competitors (#163); README Screen Map omits three shipped screens (#164).
+- Owner decisions: Sepolia support versus "Non-Goals for 1.0", and `isMetaMask`
+  naming a competitor in shipped code (#165).
+- Repo policy compliance sweep: test rerun pattern, `yarn`/`npx`, frozen
+  lockfile, undocumented Makefile targets (#166).
+- Prune the 24 stale remote feature branches (#167).
+- Remove dead exports and de-duplicate copy-pasted view helpers (#168).
 - Pre-1.0 security review of the extension (key handling, DEBUG mode policy, RPC
-  input validation) before any 1.0rc tag.
+  input validation) before any 1.0rc tag; #149 and #157 are parts of it, but the
+  review is broader than either.
+- Cut 1.0.0 once the milestone is empty, then continue tagging as milestones
+  land.
diff --git a/build.js b/build.js
index 54c1179..d738586 100644
--- a/build.js
+++ b/build.js
@@ -11,6 +11,14 @@ function ensureDir(dir) {
     fs.mkdirSync(dir, { recursive: true });
 }
 
+// DEBUG is a build-time flag, off unless explicitly requested. It is the only
+// thing that makes the hardcoded test mnemonic reachable, so the opt-in must be
+// exact: anything other than the literal "1" (unset, empty, "true", a typo)
+// produces a release build. Failing towards the safe mode is deliberate.
+function isDebugBuild() {
+    return process.env.AUTISTMASK_DEBUG === "1";
+}
+
 function getBuildInfo() {
     const pkg = JSON.parse(
         fs.readFileSync(path.join(__dirname, "package.json"), "utf8"),
@@ -47,7 +55,15 @@ async function build() {
     const buildInfo = getBuildInfo();
     console.log("Build info:", buildInfo);
 
+    const debugBuild = isDebugBuild();
+    console.log(
+        debugBuild
+            ? "Build mode: DEBUG (INSECURE - hardcoded test mnemonic, do not ship)"
+            : "Build mode: release (DEBUG off)",
+    );
+
     const define = {
+        __BUILD_DEBUG__: JSON.stringify(debugBuild),
         __BUILD_VERSION__: JSON.stringify(buildInfo.version),
         __BUILD_LICENSE__: JSON.stringify(buildInfo.license),
         __BUILD_AUTHOR__: JSON.stringify(buildInfo.author),
diff --git a/src/shared/constants.js b/src/shared/constants.js
index 1280296..7daaaf7 100644
--- a/src/shared/constants.js
+++ b/src/shared/constants.js
@@ -1,4 +1,12 @@
-const DEBUG = true;
+// DEBUG is a build-time constant injected by esbuild's define in build.js
+// (see src/shared/buildInfo.js for the same pattern). It is false unless the
+// bundle was produced with AUTISTMASK_DEBUG=1, and it is false whenever the
+// module is loaded outside a bundle (tests, plain require). It must never be
+// derived from anything the user can change at runtime: it is what gates the
+// hardcoded test mnemonic below.
+/* global __BUILD_DEBUG__ */
+const DEBUG = typeof __BUILD_DEBUG__ !== "undefined" ? __BUILD_DEBUG__ : false;
+
 const DEBUG_MNEMONIC =
     "cube evolve unfold result inch risk jealous skill hotel bulb night wreck";
 
diff --git a/src/shared/wallet.js b/src/shared/wallet.js
index ff29648..8b2dadc 100644
--- a/src/shared/wallet.js
+++ b/src/shared/wallet.js
@@ -5,6 +5,10 @@ const { Mnemonic, HDNodeWallet, Wallet } = require("ethers");
 const { DEBUG, DEBUG_MNEMONIC, BIP44_ETH_PATH } = require("./constants");
 
 function generateMnemonic() {
+    // This must stay the compile-time DEBUG constant. Do NOT switch it to
+    // isDebug() from log.js: that also ORs in the runtime debugMode flag the
+    // settings toggle drives, which would let a user of a release build turn
+    // the hardcoded, publicly known test phrase back on for real wallets.
     if (DEBUG) return DEBUG_MNEMONIC;
     const m = Mnemonic.fromEntropy(
         globalThis.crypto.getRandomValues(new Uint8Array(16)),
diff --git a/tests/wallet.test.js b/tests/wallet.test.js
new file mode 100644
index 0000000..620bd19
--- /dev/null
+++ b/tests/wallet.test.js
@@ -0,0 +1,94 @@
+// Tests for the DEBUG build flag as it gates mnemonic generation.
+//
+// The modules read the __BUILD_DEBUG__ global that esbuild replaces at bundle
+// time. Under jest the global is absent, which is exactly the release-build
+// case; the debug-build case is exercised by defining the global and
+// re-requiring the modules with a fresh registry.
+
+const WORDS_IN_12_WORD_PHRASE = 12;
+
+function loadWallet() {
+    const constants = require("../src/shared/constants");
+    const wallet = require("../src/shared/wallet");
+    const log = require("../src/shared/log");
+    return { constants, wallet, log };
+}
+
+describe("generateMnemonic in a release build", () => {
+    beforeEach(() => {
+        jest.resetModules();
+        delete globalThis.__BUILD_DEBUG__;
+    });
+
+    test("DEBUG defaults to false when the build define is absent", () => {
+        const { constants } = loadWallet();
+        expect(constants.DEBUG).toBe(false);
+    });
+
+    test("returns fresh, valid 12-word phrases that are not the test phrase", () => {
+        const { constants, wallet } = loadWallet();
+
+        const first = wallet.generateMnemonic();
+        const second = wallet.generateMnemonic();
+
+        expect(first).not.toBe(second);
+        for (const phrase of [first, second]) {
+            expect(wallet.isValidMnemonic(phrase)).toBe(true);
+            expect(phrase.split(" ")).toHaveLength(WORDS_IN_12_WORD_PHRASE);
+            expect(phrase).not.toBe(constants.DEBUG_MNEMONIC);
+        }
+    });
+
+    test("derives a usable HD wallet from the generated phrase", () => {
+        const { wallet } = loadWallet();
+
+        const { xpub, firstAddress } = wallet.hdWalletFromMnemonic(
+            wallet.generateMnemonic(),
+        );
+
+        expect(xpub.startsWith("xpub")).toBe(true);
+        expect(firstAddress).toMatch(/^0x[0-9a-fA-F]{40}$/);
+    });
+
+    test("the runtime debug toggle cannot re-enable the test phrase", () => {
+        const { constants, wallet, log } = loadWallet();
+
+        // What the settings easter-egg toggle does at runtime.
+        log.setRuntimeDebug(true);
+        expect(log.isDebug()).toBe(true);
+
+        const phrase = wallet.generateMnemonic();
+        expect(phrase).not.toBe(constants.DEBUG_MNEMONIC);
+        expect(wallet.isValidMnemonic(phrase)).toBe(true);
+        expect(phrase).not.toBe(wallet.generateMnemonic());
+
+        log.setRuntimeDebug(false);
+    });
+});
+
+describe("generateMnemonic in a debug build", () => {
+    beforeEach(() => {
+        jest.resetModules();
+        globalThis.__BUILD_DEBUG__ = true;
+    });
+
+    afterEach(() => {
+        delete globalThis.__BUILD_DEBUG__;
+    });
+
+    test("DEBUG is true and the test phrase is returned", () => {
+        const { constants, wallet } = loadWallet();
+
+        expect(constants.DEBUG).toBe(true);
+        expect(wallet.generateMnemonic()).toBe(constants.DEBUG_MNEMONIC);
+    });
+
+    test("the test phrase is itself a valid 12-word BIP-39 phrase", () => {
+        const { constants, wallet } = loadWallet();
+
+        expect(wallet.isValidMnemonic(constants.DEBUG_MNEMONIC)).toBe(true);
+        expect(constants.DEBUG_MNEMONIC.split(" ")).toHaveLength(
+            WORDS_IN_12_WORD_PHRASE,
+        );
+    });
+});