diff --git a/.agent/phases/complete/39_configurable_brand/01_config_endpoint.md b/.agent/phases/complete/39_configurable_brand/01_config_endpoint.md
new file mode 100644
index 0000000..e29bdb4
--- /dev/null
+++ b/.agent/phases/complete/39_configurable_brand/01_config_endpoint.md
@@ -0,0 +1,27 @@
+# Task 01 — `GET /api/config`
+
+**Phase:** `39_configurable_brand` · **Source:** `TODO.md:12 — "Also need a way to customize the name for 'Brain of'. Should be an env var."`
+**Story:** `.agent/user_stories/configurable-brand.md`
+
+## Objective
+A public, stateless endpoint that hands the frontend its display name (+ version) — the single source the brand layer reads.
+
+## Work
+1. `app/api/config.py` — a new router mirroring the `app/api/health.py` pattern:
+   ```python
+   @router.get("/config")
+   def app_config(settings: Settings = Depends(get_settings)) -> dict[str, str]:
+       """Public app metadata for the frontend brand layer (phase 39)."""
+       return {"app_name": settings.app_name, "version": settings.app_version}
+   ```
+   Public (no `require_admin` — the brand must render for anonymous users too, before any sign-in); stateless (A10); the response carries **exactly** these two keys (no other setting may leak in later — the test asserts the key set).
+2. `app/main.py` — register it with the other routers (`app.include_router(config_router, prefix="/api")`), before the static mount (API routes take precedence — same order as the existing routers).
+3. Tests (follow the health test's location and pattern): 200 for anonymous; default values (`"Brain of Reese"`, the current `app_version`); with an overridden `Settings` (`app_name="Brain of Testy"`) the response follows; the response key set == `{"app_name", "version"}`.
+
+## Testing & Quality
+- The tests above; full `uv run pytest` green.
+- Coverage: **>90%** on the new module (keep the handler + docstring tight so it stays covered).
+
+## Completion Criteria
+- [ ] `GET /api/config` (anonymous) → `{"app_name": "Brain of Reese", "version": "0.1.0"}` (the current default version).
+- [ ] The suite green; `uv run ruff check . && uv run pyright` clean.
diff --git a/.agent/phases/complete/39_configurable_brand/02_frontend_branding.md b/.agent/phases/complete/39_configurable_brand/02_frontend_branding.md
new file mode 100644
index 0000000..5016e00
--- /dev/null
+++ b/.agent/phases/complete/39_configurable_brand/02_frontend_branding.md
@@ -0,0 +1,34 @@
+# Task 02 — `brand.js` + de-hard-coding
+
+**Phase:** `39_configurable_brand` · **Source:** `TODO.md:12 — "Also need a way to customize the name for 'Brain of'. Should be an env var."`
+**Story:** `.agent/user_stories/configurable-brand.md`
+
+## Objective
+Every visible brand string on every page resolves from one place (`window.BOR_BRAND`, fed by `/api/config`) — the default "Brain of Reese" renders immediately, and a fetch failure falls back to the default (the page never breaks).
+
+## Work
+1. `frontend/assets/brand.js` — a new small **classic** script (vanilla, no CDN — A11; not a module, so its top level runs at parse time):
+   - Top level: `window.BOR_BRAND = "Brain of Reese"` (synchronous default — module scripts execute after parsing, so the page scripts can read it from the first line).
+   - DOM application (deferred: `if (document.readyState === "loading") document.addEventListener("DOMContentLoaded", applyBrand); else applyBrand();`):
+     1. `fetch("/api/config", { cache: "no-store" })`; on success with a non-empty `app_name`: `window.BOR_BRAND = app_name`, then:
+     2. `document.title = document.title.replaceAll("Brain of Reese", name)`.
+     3. Every `.brand-text` node: if the name starts with `"Brain of "` → `innerHTML = 'Brain of <strong>' + escapeHTML(rest) + '</strong>'` (the current look for the default name); else → `textContent = name` (plain, no bold). **HTML-escape the name** (an operator-controlled string must not inject markup).
+     4. A `TreeWalker` over the document's text nodes: replace the literal "Brain of Reese" with the name (catches the index empty-state h1 "Hey! I'm Brain of Reese." and any prose).
+     5. An attribute pass over `aria-label`, `placeholder`, and meta `content` attributes containing the literal → replace (the `#messages` aria-label "Conversation with Brain of Reese", the input label, the meta descriptions).
+   - On fetch failure: keep the default, `console.warn` (the `loadHealth` house style — progressive enhancement, never break the page).
+   - Small local `escapeHTML` helper (the `markdown.js` pattern — do not import across modules unless the build makes it easy).
+2. The templates (`frontend/index.html`, `sources.html`, `tuning.html`, `document.html`, `login.html`) — add `<script src="assets/brand.js"></script>` **before** the page's module script on every page (classic script → runs at parse time; the module scripts execute later). No other template changes — the walker + attribute pass is the single mechanism; do **not** add `data-brand` markers. The phase-33 `?v=` rewriting picks the new ref up automatically (`app/core/caching.py` matches any `src="…assets/…"`).
+3. `frontend/assets/app.js` — replace the "Brain of Reese" literals with `window.BOR_BRAND` reads: the `UI_STATE` labels (~L107: "… is thinking" / "… is answering"), `TYPING_LABEL` (~L112), the elapsed-hint aria-label (~L540). Pattern: `const brand = () => window.BOR_BRAND || "Brain of Reese";` + template strings. (Mid-turn staleness: a label set before the fetch lands keeps the old name for that turn — accepted, see the phase's locked decisions.)
+4. `frontend/assets/document.js` — the page titles (L147/152: `${doc.title} · Brain of Reese` / `"Document not found · …"`) → use the same `window.BOR_BRAND` read (document.js is a module — `window.BOR_BRAND` is set by then).
+5. `Containerfile` — add the esbuild line for the new file next to the others (L17–23 pattern, classic script like `markdown.js`): `esbuild ./assets/brand.js --minify --outfile=/out/assets/brand.js`.
+6. Verify the no-op property: with the default settings the rendered DOM text is byte-identical to pre-phase on all five pages (the replace is a no-op for the default name) — the existing suites' title/label assertions are the guard; if any assert a string this task moved onto `window.BOR_BRAND`, the default path must render the identical bytes.
+
+## Testing & Quality
+- No Python logic — the story E2E (task 03) is the gate; the existing suites (which assert the default "Brain of Reese" titles/labels against the shared conftest server) must stay green **unchanged**.
+- No CDN (rule 6): no new external tags. UI Structure Check (rule 5): no landmark/contrast change — the brand text keeps its existing classes and styling (the `innerHTML` rewrite only re-emits the same structure with the new name).
+
+## Completion Criteria
+- [ ] `BOR_APP_NAME` unset → all five pages render exactly as today (existing suites green).
+- [ ] `BOR_APP_NAME="Brain of Testy"` → title/header/greeting/labels/aria all carry the new name (asserted by the story E2E, task 03).
+- [ ] The Containerfile build includes brand.js; the asset ref is versioned like its siblings (phase 33).
+- [ ] `uv run pytest` green; `uv run ruff check . && uv run pyright` clean.
diff --git a/.agent/phases/todo/39_configurable_brand/00_phase.md b/.agent/phases/todo/39_configurable_brand/00_phase.md
new file mode 100644
index 0000000..66c02ef
--- /dev/null
+++ b/.agent/phases/todo/39_configurable_brand/00_phase.md
@@ -0,0 +1,39 @@
+# Phase 39 — Configurable app name (brand)
+
+**Source:** `TODO.md` L12 — "Also need a way to customize the name for 'Brain of'. Should be an env var."
+**Story:** `.agent/user_stories/configurable-brand.md`
+**Context:** `app/config.py` (`app_name`, already `BOR_APP_NAME`, currently used only for the OpenAPI title at `app/main.py:48`), the five templates (`frontend/*.html` — the `.brand-text` spans, the `<title>`s, the meta descriptions, the index empty-state h1, the `aria-label`s), `frontend/assets/app.js` (status labels ~L107/112, the elapsed-hint aria ~L540), `frontend/assets/document.js` (page titles L147/152), `app/api/health.py` (the public stateless endpoint pattern), `app/core/caching.py` (phase 33: `?v=` rewriting of `assets/…` refs — automatic for any new asset file), the `Containerfile` esbuild stage (explicit per-asset lines, L17–23).
+
+## Objective
+Make **one env var** (`BOR_APP_NAME`, default "Brain of Reese") drive the app's display name everywhere — titles, the header brand, the status labels, the aria text, the greeting — via a public `/api/config` endpoint + a small `brand.js`, with zero behavior change when the variable is unset.
+
+## Dependencies
+- `34_consistent_navbar` (todo — runs before this phase) — the standard five-page header (the `.brand-text` nodes this phase re-skins).
+- `01_infrastructure` (complete) — the public stateless endpoint pattern (`app/api/health.py`).
+
+## Tasks
+1. `01_config_endpoint.md` — public `GET /api/config` → `{app_name, version}` + tests.
+2. `02_frontend_branding.md` — `brand.js` + the template/JS de-hard-coding + the Containerfile build line.
+3. `03_e2e_docs_commit.md` — the story E2E (its own app instance with the overridden name), `.env.example` + README, commit, move the phase dir.
+
+## Testing & Quality
+- Unit/integration: the endpoint (200, the values, anonymous access, exactly two keys — no settings may leak later).
+- E2E (mandatory, A16): `tests/e2e/test_configurable_brand.py` — a **second** app instance booted with `BOR_APP_NAME` overridden; run in isolation.
+- Coverage: **>90%** on `app/`.
+- Regression: the default-name behavior is byte-identical — the existing suites (which assert "Brain of Reese" titles/labels against the shared conftest server) stay green **unchanged**.
+
+## Completion Criteria
+- [ ] `GET /api/config` (anonymous) → `{"app_name": "Brain of Reese", "version": "0.1.0"}` by default; the response key set is exactly `{app_name, version}`.
+- [ ] With `BOR_APP_NAME="Brain of Testy"`: the index title "Brain of Testy"; the header `.brand-text` renders `Brain of <strong>Testy</strong>`; the empty-state h1 "Hey! I'm Brain of Testy."; the `#messages` aria-label "Conversation with Brain of Testy"; the chat status label "Brain of Testy is thinking"; the other pages' titles carry the name; the document viewer title "… · Brain of Testy".
+- [ ] With the variable unset: the existing E2E + unit suites green unchanged (no rename leak).
+- [ ] `uv run pytest` green; `uv run pytest --cov=app --cov-report=term-missing` >90%; `uv run pytest tests/e2e/test_configurable_brand.py -v --no-cov` green in isolation.
+- [ ] `uv run ruff check . && uv run pyright` clean.
+- [ ] UI Structure Check (AGENTS.md rule 5) + no CDN (rule 6).
+- [ ] One `--no-gpg-sign` commit; phase directory moved to `.agent/phases/complete/`.
+
+## Locked decisions
+- **The existing `app_name` setting is the source of truth (owner permission 2026-08-26)** — `BOR_APP_NAME` (default "Brain of Reese"); no new variable, no setting rename.
+- **A11 honoured** — runtime fetch + JS application (no build-time template injection, no Jinja, no CDN); the static templates stay static.
+- **A10 honoured** — `/api/config` is public and stateless; the response carries no secrets (exactly `app_name` + `version`).
+- **Runtime fetch, brief flash accepted (owner permission 2026-08-26)** — the default name renders immediately and is replaced when `/api/config` answers (LAN latency; no re-paint machinery for in-flight turns — a mid-turn label keeps the previous name for that turn).
+- **A16/A17 honoured** — one new story E2E suite + one atomic `--no-gpg-sign` commit.
diff --git a/.agent/phases/todo/39_configurable_brand/03_e2e_docs_commit.md b/.agent/phases/todo/39_configurable_brand/03_e2e_docs_commit.md
new file mode 100644
index 0000000..25f7e3e
--- /dev/null
+++ b/.agent/phases/todo/39_configurable_brand/03_e2e_docs_commit.md
@@ -0,0 +1,27 @@
+# Task 03 — Story E2E + docs + commit
+
+**Phase:** `39_configurable_brand` · **Source:** `TODO.md:12 — "Also need a way to customize the name for 'Brain of'. Should be an env var."`
+**Story:** `.agent/user_stories/configurable-brand.md`
+
+## Objective
+The story's isolated Playwright suite against an app instance booted with the overridden name, the env docs, and the phase commit.
+
+## Work
+1. `tests/e2e/test_configurable_brand.py` (the story gate — one story, one file, run in isolation):
+   - A **second app instance** — the shared `app_server` conftest fixture keeps the default name (the other suites' title/label assertions depend on it). Copy the conftest `app_server` env block (same DB, the mock-LLM base URL, `BOR_ADMIN_PASSWORD`/`BOR_SESSION_SECRET`, `BOR_STATIC_DIR`, `BOR_RELEVANCE_THRESHOLD`) with two changes: `BOR_APP_NAME="Brain of Testy"` and a distinct port (`APP_PORT + 1` per the conftest convention). A session-scoped fixture **inside the test file**, started after `mock_llm` is available.
+   - Assertions (custom instance): index `document.title` == `"Brain of Testy"`; the `.brand-text` `innerHTML` == `Brain of <strong>Testy</strong>`; the empty-state h1 text == `"Hey! I'm Brain of Testy."`; the `#messages` `aria-label` == `"Conversation with Brain of Testy"`; the sources page title `"Sources · Brain of Testy"`; the login page title `"Sign in · Brain of Testy"`; one chat turn with a pre-token window (the `think out loud` marker) → the button label shows `"Brain of Testy is thinking"`.
+   - Default-name assertion (cheap regression in the same file): the shared conftest server's index title still == `"Brain of Reese"`.
+   - The chat-turn assertion works on the default (possibly empty) KB — a deflected answer is fine; the label assertion is pre-token, so no DB seeding is required.
+2. `.env.example` — document `BOR_APP_NAME` in the App section (the display name on all pages; default "Brain of Reese").
+3. README — the configuration section: `BOR_APP_NAME` (what it affects: titles, the header brand, the status labels, the aria text; the default; the bold-split rendering rule: names starting "Brain of " bold the remainder, any other name renders in normal weight).
+4. Regression pass: `uv run pytest` + the coverage gate (>90%) + the isolated story E2E + the suites that assert brand strings (`test_smoke.py`, `test_shared_header.py`, `test_header_consistency.py`, `test_chat_persistence.py`) green.
+5. Commit — one atomic `--no-gpg-sign` Conventional Commits commit for the whole phase (AGENTS.md rule 8), e.g. `feat(brand): configurable app name — BOR_APP_NAME drives /api/config + the frontend brand layer`; move the phase directory to `.agent/phases/complete/`.
+
+## Testing & Quality
+- The gates above are this task's quality bar (A16: one story, one isolated E2E file, coverage >90%).
+
+## Completion Criteria
+- [ ] The story E2E is green in isolation, deterministic across two consecutive runs (custom-name instance + the default-name assertion).
+- [ ] The step-4 regression list green; coverage >90%.
+- [ ] `uv run ruff check . && uv run pyright` clean.
+- [ ] One `--no-gpg-sign` commit; phase directory moved to `.agent/phases/complete/`.
diff --git a/.env.example b/.env.example
index c3a2894..6d98f44 100644
--- a/.env.example
+++ b/.env.example
@@ -4,6 +4,7 @@
 
 # --- App ---
 BOR_ENVIRONMENT=development
+# BOR_APP_NAME=Brain of Reese      # display name on all pages — titles, header brand, status labels, aria text (phase 39)
 # BOR_LOG_LEVEL=INFO
 # BOR_STATIC_DIR=frontend          # dev default; container sets /app/static
 
diff --git a/Containerfile b/Containerfile
index 543223e..6127617 100644
--- a/Containerfile
+++ b/Containerfile
@@ -20,6 +20,7 @@ RUN mkdir -p /out/assets \
     && esbuild ./assets/login.js    --bundle --minify --format=esm --target=es2022 --outfile=/out/assets/login.js \
     && esbuild ./assets/tuning.js   --bundle --minify --format=esm --target=es2022 --outfile=/out/assets/tuning.js \
     && esbuild ./assets/git-sources.js --bundle --minify --format=esm --target=es2022 --outfile=/out/assets/git-sources.js \
+    && esbuild ./assets/brand.js   --minify --outfile=/out/assets/brand.js \
     && esbuild ./assets/markdown.js --minify --outfile=/out/assets/markdown.js \
     && esbuild ./assets/styles.css  --minify --outfile=/out/assets/styles.css \
     && cp ./index.html ./sources.html ./document.html ./login.html ./tuning.html ./git-sources.html /out/
diff --git a/README.md b/README.md
index 672beb0..7d7f649 100644
--- a/README.md
+++ b/README.md
@@ -630,6 +630,7 @@ served locally (no CDN), `BOR_ENVIRONMENT=production`.
 
 | Env | Default | Meaning |
 |-----|---------|---------|
+| `BOR_APP_NAME` | `Brain of Reese` | the display name everywhere (phase 39): every page `<title>`, the header brand, the chat status labels ("… is thinking"), the empty-state greeting, and the aria/placeholder text. Served to the frontend by `GET /api/config` and applied by `assets/brand.js`; a name starting `Brain of ` keeps the bold split (`Brain of <strong>rest</strong>`), any other name renders in normal weight. Unset ⇒ byte-identical to the default |
 | `BOR_DATABASE_URL` | local compose URL | SQLAlchemy URL (psycopg) |
 | `BOR_LLM_BASE_URL` | `https://aipi.reeseapps.com/v1` | OpenAI-compatible endpoint |
 | `BOR_LLM_API_KEY` | — (falls back to `$AIPI_KEY`) | aipi API key |
diff --git a/app/api/config.py b/app/api/config.py
new file mode 100644
index 0000000..5b3a6dc
--- /dev/null
+++ b/app/api/config.py
@@ -0,0 +1,14 @@
+"""Public app metadata (display name + version) for the frontend brand layer."""
+from __future__ import annotations
+
+from fastapi import APIRouter, Depends
+
+from app.config import Settings, get_settings
+
+router = APIRouter(tags=["config"])
+
+
+@router.get("/config")
+def app_config(settings: Settings = Depends(get_settings)) -> dict[str, str]:  # noqa: B008
+    """Public app metadata for the frontend brand layer (phase 39)."""
+    return {"app_name": settings.app_name, "version": settings.app_version}
diff --git a/app/main.py b/app/main.py
index 39e541c..d4c75cf 100644
--- a/app/main.py
+++ b/app/main.py
@@ -21,6 +21,7 @@ from starlette.middleware.sessions import SessionMiddleware
 
 from app.api.auth import router as auth_router
 from app.api.chat import router as chat_router
+from app.api.config import router as config_router
 from app.api.docs import router as docs_router
 from app.api.git_sources import router as git_sources_router
 from app.api.health import router as health_router
@@ -62,6 +63,7 @@ def create_app() -> FastAPI:
 
     # API routes first so they take precedence over the catch-all static mount.
     app.include_router(health_router, prefix="/api")
+    app.include_router(config_router, prefix="/api")
     app.include_router(auth_router, prefix="/api")
     app.include_router(suggestions_router, prefix="/api")
     app.include_router(docs_router, prefix="/api")
diff --git a/frontend/assets/app.js b/frontend/assets/app.js
index 9260b1d..b09c1ec 100644
--- a/frontend/assets/app.js
+++ b/frontend/assets/app.js
@@ -47,8 +47,9 @@
  * "thinking": the UI state itself stays "thinking" (button stays
  * disabled — never stale, PLAN §7.4) while the LABELS change — the
  * button says "Calling tool…", the #send-status + typing-indicator
- * labels say what Brain is doing ("Brain of Reese is listing documents"
- * / "Brain of Reese is reading source/path"), and a visible `.tool-call`
+ * labels say what Brain is doing ("…is listing documents" /
+ * "…is reading source/path" — the name prefix resolves from
+ * window.BOR_BRAND at call time, phase 39), and a visible `.tool-call`
  * line (own icon + accent color, distinct from the brand-ink Thinking
  * block) is appended above the answer, one per call, in order.
  * Append-only like thinking: frames are tolerated in any interleaving
@@ -111,6 +112,14 @@ const banner = document.querySelector("#kb-banner");
 const bannerText = document.querySelector("#kb-banner-text");
 const versionEl = document.querySelector("#app-version");
 
+/* Phase 39: the display name resolves from one place — window.BOR_BRAND
+ * (the classic assets/brand.js sets it at parse time; its /api/config
+ * fetch refreshes it). Read LAZILY (a function, not a const string):
+ * a label set after the fetch lands carries the configured name; the
+ * literal below is only the no-config fallback — with the default name
+ * every label renders the pre-phase-39 bytes. */
+const brand = () => window.BOR_BRAND || "Brain of Reese";
+
 /* ---------- loading-feedback contract (PLAN §7.4) ----------
  * Client-side guard: a pre-token stream that produces no delta within
  * TURN_TIMEOUT_MS is treated as hung → error state + banner. It is
@@ -126,14 +135,20 @@ const UI_STATE = Object.freeze({
   error: "error",
 });
 
+/* The #send-status live-region text per UI state (PLAN §7.4). The
+ * values are builders (phase 39): the brand entries resolve brand() at
+ * call time, never at module evaluation, so a label set after the
+ * /api/config fetch lands carries the configured name. */
 const SEND_STATUS = Object.freeze({
-  [UI_STATE.idle]: "",
-  [UI_STATE.thinking]: "Brain of Reese is thinking",
-  [UI_STATE.streaming]: "Brain of Reese is answering",
-  [UI_STATE.error]: "The last question failed — try again",
+  [UI_STATE.idle]: () => "",
+  [UI_STATE.thinking]: () => `${brand()} is thinking`,
+  [UI_STATE.streaming]: () => `${brand()} is answering`,
+  [UI_STATE.error]: () => "The last question failed — try again",
 });
 
-const TYPING_LABEL = "Brain of Reese is thinking";
+/* The typing indicator's accessible label (the 10s elapsed-seconds
+ * hint updates it from this base) — built at call time (phase 39). */
+const TYPING_LABEL = () => `${brand()} is thinking`;
 const ERROR_HINT = "Try again — if this persists, check the LLM is reachable.";
 /* A turn with no answer content (an empty stream, or reasoning that
    exhausted max_tokens — phase 17) still renders a bubble, and this exact
@@ -350,7 +365,7 @@ function addTyping() {
   wrap.innerHTML = `
     <span class="avatar" aria-hidden="true">${BRAIN_AVATAR}</span>
     <div class="msg-body">
-      <div class="bubble typing" role="status" aria-label="${TYPING_LABEL}">
+      <div class="bubble typing" role="status" aria-label="${TYPING_LABEL()}">
         <span></span><span></span><span></span>
       </div>
     </div>`;
@@ -528,7 +543,7 @@ function startThinkingClock() {
     if (secs < 10) return; // hint only after 10s of pre-token silence
     const bubble = document.querySelector("#typing-indicator .bubble");
     if (bubble) {
-      bubble.setAttribute("aria-label", `Brain of Reese is still thinking (${secs}s)`);
+      bubble.setAttribute("aria-label", `${brand()} is still thinking (${secs}s)`);
     }
   }, 1000);
 }
@@ -556,7 +571,7 @@ export function setUiState(state, errorDetail = "") {
   sendBtn.disabled = inFlight;
   sendBtn.querySelector(".spinner").hidden = !inFlight;
   sendLabel.textContent = inFlight ? "Thinking…" : "Send";
-  sendStatus.textContent = SEND_STATUS[state] ?? "";
+  sendStatus.textContent = SEND_STATUS[state]?.() ?? "";
 
   if (state === UI_STATE.thinking) {
     addTyping();
@@ -963,8 +978,8 @@ async function handleSend(e) {
         if (!wrap) wrap = addMessage("brain", "");
         const toolStatus =
           name === "read_document" && argument
-            ? `Brain of Reese is reading ${argument}`
-            : "Brain of Reese is listing documents";
+            ? `${brand()} is reading ${argument}`
+            : `${brand()} is listing documents`;
         if (uiState === UI_STATE.thinking) {
           sendLabel.textContent = "Calling tool…";
           sendStatus.textContent = toolStatus;
diff --git a/frontend/assets/brand.js b/frontend/assets/brand.js
new file mode 100644
index 0000000..308cc66
--- /dev/null
+++ b/frontend/assets/brand.js
@@ -0,0 +1,134 @@
+/* Brain of Reese — brand layer (phase 39).
+ *
+ * One env var (BOR_APP_NAME) drives the display name everywhere. This
+ * small CLASSIC script is the single owner of the resolution — it is not
+ * a module, so its top level runs at parse time: window.BOR_BRAND is
+ * readable from the first line of the page's module scripts (modules
+ * execute after parsing, so a module could not guarantee this).
+ *
+ * Contract (phase 39 locked decisions — A11 no CDN, runtime fetch):
+ *   • window.BOR_BRAND = "Brain of Reese" synchronously — the default
+ *     name renders immediately, no blank flash;
+ *   • fetch("/api/config", { cache: "no-store" }) — on success with a
+ *     non-empty app_name, window.BOR_BRAND is updated and the name is
+ *     applied to the DOM:
+ *       1. document.title — global replace of the literal;
+ *       2. every .brand-text node — a name starting "Brain of " keeps
+ *          the current look (Brain of <strong>rest</strong>), any other
+ *          name renders plain (no bold); the name is HTML-escaped (an
+ *          operator-controlled string must not inject markup);
+ *       3. a TreeWalker over the document's text nodes — the literal is
+ *          replaced (the index empty-state h1 "Hey! I'm Brain of
+ *          Reese." and any other prose); script/style text nodes are
+ *          skipped so page source is never mutated;
+ *       4. an attribute pass — the aria-label / placeholder / meta
+ *          content attributes containing the literal (the #messages
+ *          aria-label, the input label, the meta descriptions).
+ *   • fetch failure / empty name → the default stays + console.warn
+ *     (the loadHealth house style: progressive enhancement, the page
+ *     never breaks).
+ *
+ * No-op property: with BOR_APP_NAME unset the /api/config answer IS the
+ * literal, so every replacement below is a byte-identical no-op.
+ */
+
+/* The synchronous default — set BEFORE any fetch, so module scripts
+   reading window.BOR_BRAND at evaluation time always find a value. */
+window.BOR_BRAND = "Brain of Reese";
+
+/* The literal the DOM passes replace — the default name. The page
+   scripts' own `window.BOR_BRAND || "Brain of Reese"` fallbacks stay in
+   sync with it. */
+const BRAND_LITERAL = "Brain of Reese";
+
+/* The name is operator-controlled: HTML-escape it before it touches
+   innerHTML (the markdown.js escape pattern — local on purpose, no
+   cross-module import for a 5-line helper). */
+function escapeHTML(s) {
+  return String(s).replace(/[&<>"']/g, (c) => ({
+    "&": "&amp;", "<": "&lt;", ">": "&gt;", '"': "&quot;", "'": "&#39;",
+  }[c]));
+}
+
+function applyBrand() {
+  fetch("/api/config", { cache: "no-store" })
+    .then((r) => (r.ok ? r.json() : Promise.reject(new Error(`HTTP ${r.status}`))))
+    .then((cfg) => {
+      const name = typeof cfg?.app_name === "string" ? cfg.app_name.trim() : "";
+      if (!name) return; // empty / missing: the default stands
+      window.BOR_BRAND = name;
+
+      // 1. The document title (global replace of the literal — covers
+      //    every page's static "<…> · Brain of Reese" titles).
+      document.title = document.title.replaceAll(BRAND_LITERAL, name);
+
+      // 2. The header brand on every page: a name starting "Brain of "
+      //    keeps the bold split (the current look), anything else
+      //    renders plain — the name is always escaped.
+      for (const el of document.querySelectorAll(".brand-text")) {
+        if (name.startsWith("Brain of ")) {
+          const rest = name.slice("Brain of ".length);
+          el.innerHTML = `Brain of <strong>${escapeHTML(rest)}</strong>`;
+        } else {
+          el.textContent = name;
+        }
+      }
+
+      // 3. Prose: a TreeWalker over the body's text nodes replaces the
+      //    literal (the empty-state h1, any other copy). Text nodes
+      //    inside <script>/<style> are rejected — the page source must
+      //    never be rewritten.
+      const walker = document.createTreeWalker(
+        document.body,
+        NodeFilter.SHOW_TEXT,
+        {
+          acceptNode(node) {
+            const tag = node.parentElement ? node.parentElement.tagName : "";
+            return tag === "SCRIPT" || tag === "STYLE"
+              ? NodeFilter.FILTER_REJECT
+              : NodeFilter.FILTER_ACCEPT;
+          },
+        },
+      );
+      const nodes = [];
+      while (walker.nextNode()) nodes.push(walker.currentNode);
+      for (const node of nodes) {
+        if (node.nodeValue && node.nodeValue.includes(BRAND_LITERAL)) {
+          node.nodeValue = node.nodeValue.replaceAll(BRAND_LITERAL, name);
+        }
+      }
+
+      // 4. Attributes: the #messages aria-label, the composer input
+      //    label, the meta descriptions — aria-label / placeholder /
+      //    meta content only, each replaced in place.
+      for (const el of document.querySelectorAll(
+        "[aria-label], [placeholder], meta[content]",
+      )) {
+        for (const attr of ["aria-label", "placeholder"]) {
+          const v = el.getAttribute(attr);
+          if (v && v.includes(BRAND_LITERAL)) {
+            el.setAttribute(attr, v.replaceAll(BRAND_LITERAL, name));
+          }
+        }
+        if (el.tagName === "META") {
+          const v = el.getAttribute("content");
+          if (v && v.includes(BRAND_LITERAL)) {
+            el.setAttribute("content", v.replaceAll(BRAND_LITERAL, name));
+          }
+        }
+      }
+    })
+    .catch((err) => {
+      // Fetch failure (or a non-JSON body): the default name stays —
+      // the page never breaks (the loadHealth house style).
+      console.warn("brand: /api/config did not answer — keeping the default name.", err);
+    });
+}
+
+/* The top level only sets the global (synchronously, at parse time);
+   the DOM passes run once the document is ready. */
+if (document.readyState === "loading") {
+  document.addEventListener("DOMContentLoaded", applyBrand);
+} else {
+  applyBrand();
+}
diff --git a/frontend/assets/document.js b/frontend/assets/document.js
index b93423b..9bd12f1 100644
--- a/frontend/assets/document.js
+++ b/frontend/assets/document.js
@@ -55,6 +55,12 @@
 
 import { fetchIsAdmin, initSharedHeader } from "./header.js";
 
+/* Phase 39: the page title's display name — window.BOR_BRAND (set at
+ * parse time by the classic assets/brand.js, refreshed from
+ * /api/config). This is a module, so the global is set by the time this
+ * evaluates; the literal is the no-config fallback only. */
+const brand = () => window.BOR_BRAND || "Brain of Reese";
+
 function fmtDate(iso) {
   try {
     return new Date(iso).toLocaleString();
@@ -180,13 +186,13 @@ if (document.querySelector("#doc-title")) {
    * the document.title (the modal keeps the page title untouched). */
   function render(doc) {
     renderDocument(doc, { titleEl, metaEl, contentEl });
-    document.title = `${doc.title} · Brain of Reese`;
+    document.title = `${doc.title} · ${brand()}`;
   }
 
   function showNotFound() {
     titleEl.textContent = "Document not found";
     titleEl.removeAttribute("title"); // no stale full-title tooltip
-    document.title = "Document not found · Brain of Reese";
+    document.title = `Document not found · ${brand()}`;
     metaEl.replaceChildren();
     contentEl.replaceChildren();
     notFoundEl.hidden = false;
diff --git a/frontend/document.html b/frontend/document.html
index 423a1eb..571ed84 100644
--- a/frontend/document.html
+++ b/frontend/document.html
@@ -153,6 +153,9 @@
     </div>
   </footer>
 
+  <!-- Phase 39: the brand layer — classic script, first on the page:
+       window.BOR_BRAND at parse time, refreshed from /api/config. -->
+  <script src="assets/brand.js"></script>
   <script src="assets/markdown.js"></script>
   <!-- Phase 19: the shared header module loads through the page script's
        own `import "./header.js"` — a hoisted import that is evaluated
diff --git a/frontend/git-sources.html b/frontend/git-sources.html
index 0db05b0..1ca9db9 100644
--- a/frontend/git-sources.html
+++ b/frontend/git-sources.html
@@ -251,6 +251,9 @@
        this body runs (the single-evaluation design: no direct
        header.js <script> tag; esbuild inlines it into the page
        bundle in the image build). -->
+  <!-- Phase 39: the brand layer — classic script, first on the page:
+       window.BOR_BRAND at parse time, refreshed from /api/config. -->
+  <script src="assets/brand.js"></script>
   <script type="module" src="/assets/git-sources.js"></script>
 </body>
 </html>
diff --git a/frontend/index.html b/frontend/index.html
index 8a10b24..63927e5 100644
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -149,6 +149,11 @@
     </div>
   </footer>
 
+  <!-- Phase 39: the brand layer — a CLASSIC script, first on every
+       page: window.BOR_BRAND is set at parse time (before the module
+       scripts evaluate) and refreshed from /api/config (a byte-
+       identical no-op for the default name). -->
+  <script src="assets/brand.js"></script>
   <script src="assets/markdown.js"></script>
   <!-- Phase 19: the shared header module loads through the page script's
        own `import "./header.js"` — a hoisted import that is evaluated
diff --git a/frontend/login.html b/frontend/login.html
index 4f1e70b..b9cd752 100644
--- a/frontend/login.html
+++ b/frontend/login.html
@@ -141,6 +141,9 @@
        <main>. The module loads through the page script's own
        `import "./header.js"` (hoisted, evaluated before the page
        script body calls initSharedHeader() at boot). -->
+  <!-- Phase 39: the brand layer — classic script, first on the page:
+       window.BOR_BRAND at parse time, refreshed from /api/config. -->
+  <script src="assets/brand.js"></script>
   <script type="module" src="/assets/login.js"></script>
 </body>
 </html>
diff --git a/frontend/sources.html b/frontend/sources.html
index f779b7e..5a30bb6 100644
--- a/frontend/sources.html
+++ b/frontend/sources.html
@@ -196,6 +196,9 @@
        Phase 26: markdown.js (the classic global renderMarkdown) loads
        BEFORE the module script — the document modal renders md
        documents through it on this page too. -->
+  <!-- Phase 39: the brand layer — classic script, first on the page:
+       window.BOR_BRAND at parse time, refreshed from /api/config. -->
+  <script src="assets/brand.js"></script>
   <script src="assets/markdown.js"></script>
   <script type="module" src="/assets/sources.js"></script>
 
diff --git a/frontend/tuning.html b/frontend/tuning.html
index 0b51821..ccdc58b 100644
--- a/frontend/tuning.html
+++ b/frontend/tuning.html
@@ -156,6 +156,9 @@
        tuning.js's own `import "./header.js"` — a hoisted import that is
        evaluated before the page script body calls initSharedHeader() at
        boot. No direct header.js <script> tag (single-evaluation design). -->
+  <!-- Phase 39: the brand layer — classic script, first on the page:
+       window.BOR_BRAND at parse time, refreshed from /api/config. -->
+  <script src="assets/brand.js"></script>
   <script src="assets/markdown.js"></script>
   <script type="module" src="/assets/tuning.js"></script>
 </body>
diff --git a/tests/e2e/test_configurable_brand.py b/tests/e2e/test_configurable_brand.py
new file mode 100644
index 0000000..6dd8eaf
--- /dev/null
+++ b/tests/e2e/test_configurable_brand.py
@@ -0,0 +1,235 @@
+"""Phase 39 E2E (Playwright): the configurable app name (``BOR_APP_NAME``).
+
+Story: ``.agent/user_stories/configurable-brand.md``
+Run in isolation (DB must be up: ``podman compose up -d db``):
+
+    uv run pytest tests/e2e/test_configurable_brand.py -v --no-cov
+
+Contract under test (owner ask — "a way to customize the name for
+'Brain of'. Should be an env var"):
+
+* one env var (``BOR_APP_NAME``, default "Brain of Reese") drives the
+  display name on EVERY page — the ``<title>``s, the header
+  ``.brand-text`` brand, the empty-state greeting, the ``#messages``
+  aria-label, and the chat status labels — via the public
+  ``GET /api/config`` + the classic ``assets/brand.js`` layer;
+* a name starting ``"Brain of "`` keeps the bold split (``Brain of
+  <strong>rest</strong>``); the name is HTML-escaped (the story's
+  acceptance criteria, AC-2);
+* with the variable UNSET the app is byte-identical to today — the
+  shared conftest server (the default name every other suite's
+  title/label assertions depend on) still renders "Brain of Reese".
+
+Determinism note: this story needs a SECOND app instance — the shared
+conftest server keeps the default name, so ``testy_server`` boots the
+same env block (same DB, the mock-LLM base URL, the admin auth, the
+static dir, the mock-calibrated threshold) with exactly two changes:
+``BOR_APP_NAME="Brain of Testy"`` and port ``APP_PORT + 1``. Every
+assertion is settled-state: Playwright's ``expect`` retries ride out
+the brand.js ``/api/config`` fetch (the name is applied asynchronously
+after the fetch answers). The one chat turn is pre-token-labeled — the
+``think out loud`` marker makes the mock stream ~2.7k chars of
+reasoning at 12 chars / 0.02 s (~4.6 s) before the first content frame,
+so the "… is thinking" label is stable for the whole window regardless
+of what the turn answers (grounded or deflected — no DB seeding
+needed).
+
+Test → story mapping (Playwright Mapping Rule):
+1. ``test_api_config_serves_both_names``
+2. ``test_index_carries_the_custom_brand``
+3. ``test_other_pages_titles_carry_the_name``
+4. ``test_chat_status_label_uses_custom_name_pre_token``
+5. ``test_shared_server_keeps_the_default_name``
+"""
+from __future__ import annotations
+
+import os
+import subprocess
+import sys
+from collections.abc import Iterator
+
+import httpx
+import pytest
+from playwright.sync_api import Page, expect
+
+from e2e.conftest import (
+    ADMIN_PASSWORD,
+    APP_PORT,
+    REPO,
+    SESSION_SECRET,
+    USE_REAL_LLM,
+    _wait_http,
+)
+
+TESTY_PORT = APP_PORT + 1
+TESTY_URL = f"http://127.0.0.1:{TESTY_PORT}"
+TESTY_NAME = "Brain of Testy"
+DEFAULT_NAME = "Brain of Reese"
+
+
+def expect_inner_html(page: Page, selector: str, expected: str, timeout: int = 15_000) -> None:
+    """Retrying innerHTML equality (Playwright's Python API ships no
+    ``to_have_inner_html`` assertion). The brand layer applies the name
+    when its ``/api/config`` fetch answers, so the check must poll —
+    ``wait_for_function`` does, on Playwright's own retry clock."""
+    page.wait_for_function(
+        """([sel, expected]) => {
+            const el = document.querySelector(sel);
+            return el !== null && el.innerHTML === expected;
+        }""",
+        arg=[selector, expected],
+        timeout=timeout,
+    )
+
+
+@pytest.fixture(scope="session")
+def testy_server(mock_llm: int) -> Iterator[str]:
+    """A SECOND app instance, booted with the overridden name.
+
+    The shared conftest ``app_server`` keeps the default name (every
+    other suite's title/label assertions depend on it) — so this
+    fixture copies its env block verbatim (same DB, the mock-LLM base
+    URL, ``BOR_ADMIN_PASSWORD``/``BOR_SESSION_SECRET``,
+    ``BOR_STATIC_DIR``, ``BOR_RELEVANCE_THRESHOLD``) with exactly two
+    changes: ``BOR_APP_NAME="Brain of Testy"`` and a distinct port
+    (``APP_PORT + 1`` per the conftest convention). Started after
+    ``mock_llm`` is available (its fixture dependency).
+    """
+    env = dict(os.environ)
+    env.pop("DEBUGPY", None)
+    env["BOR_ENVIRONMENT"] = "e2e"
+    env["BOR_STATIC_DIR"] = str(REPO / "frontend")
+    env["BOR_LLM_BASE_URL"] = (
+        "https://aipi.reeseapps.com/v1"
+        if USE_REAL_LLM
+        else f"http://127.0.0.1:{mock_llm}/v1"
+    )
+    # The mock's token-overlap embeddings have their own score
+    # distribution — the same mock-calibrated threshold as the shared
+    # instance, so this suite's turn behaves like every other story's.
+    env["BOR_RELEVANCE_THRESHOLD"] = "0.30"
+    env.setdefault(
+        "BOR_DATABASE_URL",
+        "postgresql+psycopg://reese:reese@localhost:5432/brain_of_reese",
+    )
+    # Phase 16: admin auth must be set or create_app() refuses to boot.
+    env["BOR_ADMIN_PASSWORD"] = ADMIN_PASSWORD
+    env["BOR_SESSION_SECRET"] = SESSION_SECRET
+    # The phase-39 override — the whole story:
+    env["BOR_APP_NAME"] = TESTY_NAME
+    proc = subprocess.Popen(
+        [sys.executable, "-m", "uvicorn", "app.main:app",
+         "--host", "127.0.0.1", "--port", str(TESTY_PORT), "--log-level", "warning"],
+        cwd=REPO,
+        env=env,
+    )
+    try:
+        _wait_http(f"{TESTY_URL}/api/health")
+        yield TESTY_URL
+    finally:
+        proc.terminate()
+        try:
+            proc.wait(timeout=10)
+        except subprocess.TimeoutExpired:
+            proc.kill()
+
+
+# ---------------------------------------------------------------------------
+# 1. The endpoint the brand layer reads — overridden on the second
+#    instance, default on the shared one
+# ---------------------------------------------------------------------------
+
+
+def test_api_config_serves_both_names(testy_server: str, app_server: str) -> None:
+    r = httpx.get(f"{TESTY_URL}/api/config", timeout=5)
+    assert r.status_code == 200
+    body = r.json()
+    assert set(body) == {"app_name", "version"}
+    assert body["app_name"] == TESTY_NAME
+
+    # The shared conftest instance keeps the default (the other
+    # suites' title/label contract rides on it).
+    r2 = httpx.get(f"{app_server}/api/config", timeout=5)
+    assert r2.status_code == 200
+    assert r2.json()["app_name"] == DEFAULT_NAME
+
+
+# ---------------------------------------------------------------------------
+# 2. The chat page — title, header brand, greeting, stream aria-label
+# ---------------------------------------------------------------------------
+
+
+def test_index_carries_the_custom_brand(page: Page, testy_server: str) -> None:
+    page.goto(testy_server + "/")
+    # The brand layer applies the name when /api/config answers — the
+    # retrying expectations ride out that fetch.
+    expect(page).to_have_title(TESTY_NAME, timeout=15_000)
+    # The "Brain of …" name keeps the bold split (AC-2) — and the name
+    # arrives escaped (Testy has no special characters, but the markup
+    # shape is the contract).
+    expect_inner_html(page, ".brand-text", "Brain of <strong>Testy</strong>")
+    # The empty-state greeting (the TreeWalker prose pass).
+    expect(page.locator("#empty-state h1")).to_have_text(
+        f"Hey! I'm {TESTY_NAME}.", timeout=15_000
+    )
+    # The message stream's accessible label (the attribute pass).
+    expect(page.locator("#messages")).to_have_attribute(
+        "aria-label", f"Conversation with {TESTY_NAME}", timeout=15_000
+    )
+
+
+# ---------------------------------------------------------------------------
+# 3. The other pages — their <title>s carry the name too
+# ---------------------------------------------------------------------------
+
+
+def test_other_pages_titles_carry_the_name(page: Page, testy_server: str) -> None:
+    page.goto(testy_server + "/sources.html")
+    expect(page).to_have_title(f"Sources · {TESTY_NAME}", timeout=15_000)
+
+    page.goto(testy_server + "/login.html")
+    expect(page).to_have_title(f"Sign in · {TESTY_NAME}", timeout=15_000)
+
+
+# ---------------------------------------------------------------------------
+# 4. The chat status label — a pre-token turn on the custom instance
+# ---------------------------------------------------------------------------
+
+
+def test_chat_status_label_uses_custom_name_pre_token(
+    page: Page, testy_server: str, db_ready: None
+) -> None:
+    page.goto(testy_server + "/")
+    expect(page.locator("#send-btn")).to_be_enabled(timeout=15_000)
+
+    # The ``think out loud`` marker (mock_llm.py) makes the answer
+    # stream ~2.7k chars of reasoning FIRST — the pre-token window.
+    # Works on the default (possibly empty) KB: a deflected answer is
+    # fine, the label assertion is pre-token, no seeding required.
+    page.fill("#message-input", "think out loud — what is the capital of France?")
+    page.click("#send-btn")
+
+    # The pre-token status label carries the configured name (the
+    # ~4.6 s reasoning stream keeps the state "thinking" — the label
+    # is stable for the whole window).
+    expect(page.locator("#send-status")).to_have_text(
+        f"{TESTY_NAME} is thinking", timeout=15_000
+    )
+
+    # The turn always finishes — the button is never left stale
+    # (PLAN §7.4), whatever the turn answered.
+    expect(page.locator("#send-label")).to_have_text("Send", timeout=60_000)
+
+
+# ---------------------------------------------------------------------------
+# 5. The no-op regression — the shared default-name instance is
+#    byte-identical to today
+# ---------------------------------------------------------------------------
+
+
+def test_shared_server_keeps_the_default_name(page: Page, app_server: str) -> None:
+    page.goto(app_server + "/")
+    expect(page).to_have_title(DEFAULT_NAME, timeout=15_000)
+    # With the variable unset the brand pass is a no-op: the header
+    # renders exactly the pre-phase-39 markup.
+    expect_inner_html(page, ".brand-text", "Brain of <strong>Reese</strong>")
diff --git a/tests/integration/test_api.py b/tests/integration/test_api.py
index 1a5a111..3b6e7df 100644
--- a/tests/integration/test_api.py
+++ b/tests/integration/test_api.py
@@ -17,6 +17,35 @@ def test_health_reports_ok(client) -> None:
     assert body["version"]
 
 
+def test_config_returns_default_app_metadata(client) -> None:
+    """GET /api/config is public (anonymous) and returns exactly two keys."""
+    r = client.get("/api/config")
+    assert r.status_code == 200
+    body = r.json()
+    assert set(body) == {"app_name", "version"}
+    assert body["app_name"] == "Brain of Reese"
+    assert body["version"] == get_settings().app_version
+
+
+def test_config_follows_overridden_app_name(client) -> None:
+    """GET /api/config reflects a Settings override (e.g. BOR_APP_NAME)."""
+    from app.config import Settings
+    from app.main import app as fastapi_app
+
+    fastapi_app.dependency_overrides[get_settings] = lambda: Settings(
+        app_name="Brain of Testy"
+    )
+    try:
+        r = client.get("/api/config")
+        assert r.status_code == 200
+        body = r.json()
+        assert set(body) == {"app_name", "version"}
+        assert body["app_name"] == "Brain of Testy"
+        assert body["version"] == "0.1.0"
+    finally:
+        fastapi_app.dependency_overrides.clear()
+
+
 def test_suggestions_returns_list(client) -> None:
     r = client.get("/api/suggestions")
     assert r.status_code == 200
diff --git a/tests/unit/test_frontend_brand.py b/tests/unit/test_frontend_brand.py
new file mode 100644
index 0000000..8639eb2
--- /dev/null
+++ b/tests/unit/test_frontend_brand.py
@@ -0,0 +1,173 @@
+"""Unit: the phase-39 brand layer (BOR_APP_NAME → window.BOR_BRAND).
+
+No Python logic exists for this task — the behavior lives in
+``frontend/assets/brand.js`` + the templates + the page scripts, and it
+is E2E-gated by the story suite (task 03). Like the other
+frontend-adjacent unit files, this module pins the JS markers the story
+depends on, so a silent regression in the brand layer is caught without
+a browser.
+"""
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+FRONTEND = Path(__file__).resolve().parents[2] / "frontend"
+ROOT = FRONTEND.parent
+BRAND_JS = FRONTEND / "assets" / "brand.js"
+APP_JS = FRONTEND / "assets" / "app.js"
+DOCUMENT_JS = FRONTEND / "assets" / "document.js"
+CONTAINERFILE = ROOT / "Containerfile"
+
+#: Every page in the app ships the brand layer (phase 39: "every visible
+#: brand string on every page resolves from one place").
+HTML_PAGES = (
+    "index.html",
+    "sources.html",
+    "tuning.html",
+    "document.html",
+    "login.html",
+    "git-sources.html",
+)
+
+
+def _text(path: Path) -> str:
+    return path.read_text(encoding="utf-8")
+
+
+def test_brand_js_is_a_classic_script_with_synchronous_default() -> None:
+    """brand.js is NOT a module (its top level must run at parse time,
+    before the page's module scripts evaluate) and sets window.BOR_BRAND
+    synchronously, BEFORE the /api/config fetch starts."""
+    js = _text(BRAND_JS)
+    assert not re.search(r"^\s*import\s", js, re.M), (
+        "brand.js must be a classic script — no import statements"
+    )
+    assert not re.search(r"^\s*export\s", js, re.M), (
+        "brand.js must be a classic script — no export statements"
+    )
+    default_idx = js.find('window.BOR_BRAND = "Brain of Reese"')
+    fetch_idx = js.find('fetch("/api/config"')
+    assert 0 <= default_idx < fetch_idx, (
+        "the default name must be set at top level before the fetch"
+    )
+
+
+def test_brand_js_fetches_api_config_no_store() -> None:
+    """The single source of the name is GET /api/config, never cached —
+    a renamed app must not serve a stale name from the HTTP cache — and
+    a fetch failure only warns (the loadHealth house style: the page
+    never breaks)."""
+    js = _text(BRAND_JS)
+    assert 'fetch("/api/config", { cache: "no-store" })' in js
+    assert "console.warn" in js
+
+
+def test_brand_js_defers_dom_application_until_ready() -> None:
+    """The DOM passes run on DOMContentLoaded while parsing, otherwise
+    immediately (the script sits at the end of <body>)."""
+    js = _text(BRAND_JS)
+    assert 'document.readyState === "loading"' in js
+    assert 'document.addEventListener("DOMContentLoaded", applyBrand)' in js
+
+
+def test_brand_js_reskins_title_brand_text_prose_and_attributes() -> None:
+    """The four DOM passes (phase 39 task 02): the document title,
+    every .brand-text (bold split for "Brain of …" names, plain text
+    otherwise — the name is HTML-escaped before innerHTML), a
+    TreeWalker over the text nodes (script/style nodes rejected — the
+    page source is never rewritten), and the aria-label / placeholder /
+    meta content attributes."""
+    js = _text(BRAND_JS)
+    assert "document.title.replaceAll" in js
+    assert ".brand-text" in js
+    assert 'name.startsWith("Brain of ")' in js
+    assert "escapeHTML" in js, "the name must be escaped before innerHTML"
+    assert "el.textContent = name" in js, "non-'Brain of ' names render plain"
+    assert "document.createTreeWalker" in js
+    assert "NodeFilter.SHOW_TEXT" in js
+    assert 'tag === "SCRIPT" || tag === "STYLE"' in js
+    assert "replaceAll(BRAND_LITERAL, name)" in js
+    for marker in ('"aria-label"', '"placeholder"', "meta[content]"):
+        assert marker in js, f"the attribute pass must cover {marker}"
+
+
+def test_page_scripts_keep_the_default_literal_exactly_once() -> None:
+    """The fallback literal lives in the page scripts' brand() reads —
+    exactly one copy per file (a second copy could drift out of sync)."""
+    assert _text(APP_JS).count('"Brain of Reese"') == 1, (
+        "app.js: the literal must appear only in the brand() fallback"
+    )
+    assert _text(DOCUMENT_JS).count('"Brain of Reese"') == 1, (
+        "document.js: the literal must appear only in the brand() fallback"
+    )
+
+
+def test_app_js_labels_resolve_the_name_at_call_time() -> None:
+    """Phase 39 task 02: the status labels, the typing label, the
+    elapsed-seconds hint and the tool labels read window.BOR_BRAND
+    through brand() — at CALL time, so a label set after /api/config
+    lands carries the configured name (a module-level const would
+    freeze the default)."""
+    js = _text(APP_JS)
+    assert 'const brand = () => window.BOR_BRAND || "Brain of Reese";' in js
+    assert "`${brand()} is thinking`" in js
+    assert "`${brand()} is answering`" in js
+    assert "`${brand()} is still thinking (${secs}s)`" in js
+    assert "`${brand()} is reading ${argument}`" in js
+    assert "`${brand()} is listing documents`" in js
+    # The frozen module-level literals must be gone (stale-name bug).
+    assert '"Brain of Reese is thinking"' not in js
+    assert '"Brain of Reese is answering"' not in js
+
+
+def test_document_js_titles_resolve_the_name() -> None:
+    """The viewer page titles (render + not-found) carry the resolved
+    name — the module sets them itself, so it must use brand() (the
+    static document.html title is handled by the brand.js title pass)."""
+    js = _text(DOCUMENT_JS)
+    assert 'document.title = `${doc.title} · ${brand()}`' in js
+    assert 'document.title = `Document not found · ${brand()}`' in js
+    assert 'window.BOR_BRAND || "Brain of Reese"' in js
+
+
+def test_every_page_loads_brand_js_before_its_module_script() -> None:
+    """All pages load brand.js as a CLASSIC script, before the page's
+    module script (modules execute after parsing — the synchronous
+    default must be set first)."""
+    for page in HTML_PAGES:
+        html = _text(FRONTEND / page)
+        brand_idx = html.find('<script src="assets/brand.js"></script>')
+        module_idx = html.find('<script type="module"')
+        assert brand_idx != -1, f"{page}: brand.js must load"
+        assert module_idx != -1, f"{page}: the page module must load"
+        assert brand_idx < module_idx, (
+            f"{page}: brand.js must load BEFORE the module script"
+        )
+        assert 'type="module"' not in html[brand_idx : brand_idx + 60], (
+            f"{page}: brand.js must be a classic script"
+        )
+
+
+def test_containerfile_builds_brand_js_like_its_classic_sibling() -> None:
+    """The image build minifies brand.js (classic script — minify only,
+    no --bundle, exactly like markdown.js) so the container serves it."""
+    cf = _text(CONTAINERFILE)
+    lines = [ln for ln in cf.splitlines() if "brand.js" in ln]
+    assert len(lines) == 1, "one esbuild line for brand.js"
+    line = lines[0]
+    assert "esbuild ./assets/brand.js" in line
+    assert "--minify" in line
+    assert "--bundle" not in line, (
+        "classic script: minify only (the markdown.js pattern)"
+    )
+    assert "--outfile=/out/assets/brand.js" in line
+
+
+def test_no_cdn_in_the_brand_layer() -> None:
+    """AGENTS.md rule 6: the brand layer adds no external reference."""
+    js = _text(BRAND_JS)
+    assert "http://" not in js and "https://" not in js
+    for page in HTML_PAGES:
+        html = _text(FRONTEND / page)
+        assert 'src="https://' not in html and 'href="https://' not in html
diff --git a/tests/unit/test_frontend_feedback.py b/tests/unit/test_frontend_feedback.py
index ec3cc63..e85f8ee 100644
--- a/tests/unit/test_frontend_feedback.py
+++ b/tests/unit/test_frontend_feedback.py
@@ -47,9 +47,18 @@ def test_state_machine_has_all_four_states() -> None:
 
 def test_typing_indicator_contract_strings() -> None:
     """The indicator's accessible label and the 10s elapsed-seconds hint
-    are the strings screen readers (and the E2E) rely on."""
+    are the strings screen readers (and the E2E) rely on.
+
+    Phase 39: the label is BUILT at call time from window.BOR_BRAND
+    (the classic brand.js layer) — `TYPING_LABEL()` — with the default
+    name as the only fallback, so the default path renders the same
+    bytes as before."""
     js = _js()
-    assert 'TYPING_LABEL = "Brain of Reese is thinking"' in js
+    assert "TYPING_LABEL = () =>" in js, "the label must be built at call time (phase 39)"
+    assert "`${brand()} is thinking`" in js, "the label must resolve the name via brand()"
+    assert 'window.BOR_BRAND || "Brain of Reese"' in js, (
+        "the no-config fallback must keep the default name"
+    )
     assert "still thinking" in js, "elapsed-seconds hint must update the aria label"
     assert "secs < 10" in js, "the hint must only appear after 10s of silence"
     assert "role=\"status\"" in js, "typing bubble must be role=status"
diff --git a/tests/unit/test_frontend_tool_states.py b/tests/unit/test_frontend_tool_states.py
index fea8bcd..d279e09 100644
--- a/tests/unit/test_frontend_tool_states.py
+++ b/tests/unit/test_frontend_tool_states.py
@@ -54,15 +54,16 @@ def test_tool_branch_is_a_first_class_turn_branch() -> None:
 
 def test_calling_tool_label_strings() -> None:
     """The 'calling tool' label strings the story keys off: the button
-    text and the status/typing-indicator labels (plain literals —
-    phase 39 centralizes brand strings; no helper here)."""
+    text and the status/typing-indicator labels. Phase 39 centralizes
+    the brand prefix: the name resolves from window.BOR_BRAND at call
+    time via brand() (the default name renders the same bytes)."""
     js = _js()
     tool_idx = js.find('ev.type === "tool"')
     delta_idx = js.find('ev.type === "delta"')
     branch = js[tool_idx:delta_idx]
     assert '"Calling tool…"' in branch, "the button carries the calling-tool text"
-    assert '"Brain of Reese is listing documents"' in branch
-    assert "Brain of Reese is reading ${argument}" in branch
+    assert "`${brand()} is listing documents`" in branch
+    assert "`${brand()} is reading ${argument}`" in branch
     assert "sendStatus.textContent = toolStatus" in branch, (
         "the #send-status live region announces what Brain is doing"
     )