diff --git a/.gitignore b/.gitignore
index 51af032..3392e8c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,4 @@ __pycache__/
 data/
 .venv/
 .DS_Store
+.env.bak-*
diff --git a/README.md b/README.md
index 58a49f8..05aeffb 100644
--- a/README.md
+++ b/README.md
@@ -45,26 +45,34 @@ Then open http://127.0.0.1:8123.
 ## Tests
 
 ```sh
-.venv/bin/python -m tests.test_api          # 122 checks, in-process
-.venv/bin/python -m tests.test_concurrency  # 12 checks, against a real uvicorn
+.venv/bin/python -m tests.test_api          # 166 checks, in-process
+.venv/bin/python -m tests.test_concurrency  # 15 checks, against a real uvicorn
 ```
 
 `test_api` exercises the API end to end against a throwaway database — the auth
 gate and session-token signing, nested categories and locations, search across
 every indexed field, filter rollups, stock adjustment and history, patch
 semantics including explicit nulls, taxonomy cycle rejection, security headers
-and asset versioning, and login throttling.
+and asset versioning, login throttling, and the full password-management flow
+including scrypt hashing, session invalidation and the recovery CLI.
 
 `test_concurrency` needs a real server process, because a lost update only shows
 up when two requests genuinely overlap inside SQLite. It fires overlapping
 adjustments, patches and creates at one part and asserts the stock log always
-sums to the stored quantity.
+sums to the stored quantity, and races taxonomy renames against reads to check
+the search index never describes a name the tree no longer has.
 
 ## Configuration
 
+The password is **managed from the app**, not from a config file. `PARTS_PASSWORD`
+is only the bootstrap credential: it works until a password is set through the
+UI, and is ignored from then on (otherwise "changing" the password would leave
+the old one working). The stored password is a salted scrypt hash in the
+`settings` table, which lives in the `/data` volume and survives rebuilds.
+
 | Variable | Meaning |
 |---|---|
-| `PARTS_PASSWORD` | The single shared password. Required when auth is on. |
+| `PARTS_PASSWORD` | Bootstrap password, used only until one is set in the app. |
 | `PARTS_SECRET` | Signing key for the session cookie. `openssl rand -hex 32`. |
 | `PARTS_SESSION_DAYS` | Session lifetime, default 30. |
 | `PARTS_AUTH` | `off` disables the login gate (LAN-only use). |
@@ -73,9 +81,11 @@ sums to the stored quantity.
 | `PARTS_LOGIN_WINDOW` | Throttle window in seconds, default 300. |
 | `PARTS_SECURE_COOKIE` | `auto` (default) trusts `X-Forwarded-Proto`; `on`/`off` force it. |
 
-Rotating `PARTS_PASSWORD` alone does **not** invalidate existing sessions when
-`PARTS_SECRET` is set independently — the cookie is signed with the secret.
-Rotate both to revoke every outstanding cookie.
+Every token carries a session epoch. Changing the password bumps it, which
+invalidates every outstanding cookie at once while re-issuing one for the
+browser that made the change — so a password change really does sign out other
+devices, with no need to touch `PARTS_SECRET` on the host. **Sign out other
+devices** in Settings bumps the epoch on its own.
 
 Failed logins are throttled on a **global** window rather than per source
 address. Caddy appends to `X-Forwarded-For` instead of replacing it, so the
@@ -90,11 +100,16 @@ Lives at `/home/jay/srv/parts/` on `.8` and follows the same conventions as the
 other services there — `build: .`, external `caddy_web` network, named volume
 for `/data`.
 
+`~/srv/parts` is a checkout of this repository, so deploying is a pull:
+
 ```sh
 ssh jay@192.168.50.8
-cd ~/srv/parts && sudo docker compose up -d --build
+cd ~/srv/parts && git pull && docker compose up -d --build
 ```
 
+`.env` is untracked and gitignored, so it survives the pull. `~/srv` (the infra
+repo) ignores `parts/`, since this directory is its own repository.
+
 The database is in the `parts_parts_data` docker volume, which survives
 rebuilds.
 
@@ -135,6 +150,22 @@ The "what could I build with what I'm holding?" idea is meant to arrive as
 another consumer of these endpoints — the arbiter on `.8` already has the lane
 routing and typed-action machinery for it — rather than as a fork of them.
 
+## Passwords
+
+Open **Settings** (the gear in the header) and use the Password section. It asks
+for the current password, takes a new one twice, and signs out every other
+device. Until a password has been set in the app, a banner says so.
+
+The only reason to touch a terminal is a forgotten password:
+
+```sh
+docker exec -it parts python -m app.admin set-password    # prompts, twice
+docker exec parts python -m app.admin show-status         # where the password comes from
+docker exec parts python -m app.admin clear-password      # fall back to PARTS_PASSWORD
+```
+
+Each of those signs out every session too.
+
 ## Hardening notes
 
 Responses carry `X-Content-Type-Options`, `X-Frame-Options`, `Referrer-Policy`
diff --git a/app/admin.py b/app/admin.py
new file mode 100644
index 0000000..41f2ec8
--- /dev/null
+++ b/app/admin.py
@@ -0,0 +1,65 @@
+"""Recovery CLI.
+
+Everyday password changes happen in the UI. This exists for the one case the UI
+cannot help with — a forgotten password — and for the initial handover.
+
+    docker exec -it parts python -m app.admin set-password
+    docker exec parts python -m app.admin show-status
+"""
+
+import getpass
+import sys
+
+from . import auth, db
+
+
+def set_password(argv):
+    password = argv[0] if argv else None
+    if password is None:
+        password = getpass.getpass("New password: ")
+        if password != getpass.getpass("Repeat: "):
+            print("Passwords did not match.", file=sys.stderr)
+            return 1
+    problem = auth.password_problem(password)
+    if problem:
+        print(problem, file=sys.stderr)
+        return 1
+    with db.session() as conn:
+        auth.set_password(conn, password)
+    print("Password set. All existing sessions have been signed out.")
+    return 0
+
+
+def clear_password(_argv):
+    """Fall back to the PARTS_PASSWORD environment variable again."""
+    with db.session() as conn:
+        conn.execute("DELETE FROM settings WHERE key = ?", (auth.PASSWORD_KEY,))
+        auth.bump_epoch(conn)
+    print("Stored password cleared; PARTS_PASSWORD from the environment is live again.")
+    print("All existing sessions have been signed out.")
+    return 0
+
+
+def show_status(_argv):
+    with db.session() as conn:
+        stored = auth.stored_hash(conn)
+        print("password source :", "database (set in the app)" if stored else "PARTS_PASSWORD env var")
+        print("session epoch   :", auth.current_epoch(conn))
+        print("auth enabled    :", auth.auth_enabled())
+    return 0
+
+
+COMMANDS = {"set-password": set_password, "clear-password": clear_password, "show-status": show_status}
+
+
+def main(argv=None):
+    argv = list(sys.argv[1:] if argv is None else argv)
+    if not argv or argv[0] not in COMMANDS:
+        print("usage: python -m app.admin {" + "|".join(COMMANDS) + "}", file=sys.stderr)
+        return 2
+    db.init()
+    return COMMANDS[argv[0]](argv[1:])
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/app/auth.py b/app/auth.py
index 24aac2c..ea9c9a4 100644
--- a/app/auth.py
+++ b/app/auth.py
@@ -9,10 +9,13 @@ import base64
 import hashlib
 import hmac
 import os
+import secrets
 import threading
 import time
 
-from fastapi import Cookie, HTTPException, Request
+from fastapi import Cookie, Depends, HTTPException, Request
+
+from . import db
 
 COOKIE_NAME = "parts_session"
 DIGEST_SIZE = hashlib.sha256().digest_size
@@ -46,13 +49,103 @@ def session_days() -> int:
     return _env_int("PARTS_SESSION_DAYS", 30)
 
 
-def check_password(candidate: str) -> bool:
+# --- stored password --------------------------------------------------------
+#
+# The password lives in the database, not the environment, so it can be changed
+# from the UI and survives a container rebuild (it is in the /data volume).
+# PARTS_PASSWORD is only the bootstrap credential: it works until a password has
+# been set through the app, and is ignored from then on — otherwise "changing"
+# the password would leave the old one working.
+
+PASSWORD_KEY = "password_hash"
+EPOCH_KEY = "session_epoch"
+MIN_PASSWORD_LENGTH = 8
+
+_SCRYPT_N = 1 << 14
+_SCRYPT_R = 8
+_SCRYPT_P = 1
+_SCRYPT_MAXMEM = 64 * 1024 * 1024
+
+
+def hash_password(password: str) -> str:
+    salt = secrets.token_bytes(16)
+    digest = hashlib.scrypt(
+        password.encode(), salt=salt, n=_SCRYPT_N, r=_SCRYPT_R, p=_SCRYPT_P,
+        dklen=32, maxmem=_SCRYPT_MAXMEM,
+    )
+    return "scrypt${}${}${}${}${}".format(
+        _SCRYPT_N, _SCRYPT_R, _SCRYPT_P,
+        base64.b64encode(salt).decode(), base64.b64encode(digest).decode(),
+    )
+
+
+def verify_hash(password: str, stored: str) -> bool:
+    try:
+        scheme, n, r, pp, salt_b64, digest_b64 = stored.split("$")
+        if scheme != "scrypt":
+            return False
+        digest = hashlib.scrypt(
+            password.encode(), salt=base64.b64decode(salt_b64),
+            n=int(n), r=int(r), p=int(pp), dklen=len(base64.b64decode(digest_b64)),
+            maxmem=_SCRYPT_MAXMEM,
+        )
+        return hmac.compare_digest(digest, base64.b64decode(digest_b64))
+    except Exception:
+        return False
+
+
+def stored_hash(conn) -> str | None:
+    return db.get_setting(conn, PASSWORD_KEY)
+
+
+def using_bootstrap_password(conn) -> bool:
+    """True while the env-provided password is still the live one."""
+    return stored_hash(conn) is None
+
+
+def check_password(conn, candidate: str) -> bool:
+    stored = stored_hash(conn)
+    if stored:
+        return verify_hash(candidate, stored)
     expected = _env("PARTS_PASSWORD")
     if not expected:
         return False
     return hmac.compare_digest(candidate.encode(), expected.encode())
 
 
+def set_password(conn, new_password: str):
+    """Store a new password and invalidate every outstanding session."""
+    db.set_setting(conn, PASSWORD_KEY, hash_password(new_password))
+    bump_epoch(conn)
+
+
+def password_problem(new_password: str) -> str | None:
+    if len(new_password) < MIN_PASSWORD_LENGTH:
+        return f"Password must be at least {MIN_PASSWORD_LENGTH} characters"
+    if not new_password.strip():
+        return "Password must not be blank"
+    return None
+
+
+# --- session epoch ----------------------------------------------------------
+#
+# Baked into every token. Bumping it invalidates all outstanding cookies at
+# once, which is what makes "change my password" and "sign out everywhere"
+# work without having to rotate PARTS_SECRET by hand on the host.
+
+def current_epoch(conn) -> int:
+    try:
+        return int(db.get_setting(conn, EPOCH_KEY, "0") or "0")
+    except ValueError:
+        return 0
+
+
+def bump_epoch(conn) -> int:
+    epoch = current_epoch(conn) + 1
+    db.set_setting(conn, EPOCH_KEY, epoch)
+    return epoch
+
+
 # --- session tokens ---------------------------------------------------------
 #
 # The signature is raw HMAC bytes, which can contain any byte value including
@@ -61,14 +154,14 @@ def check_password(candidate: str) -> bool:
 # split in the wrong place and failed their own validator. The digest is a fixed
 # 32 bytes, so slice by length instead of looking for a delimiter.
 
-def issue_token() -> str:
+def issue_token(conn) -> str:
     expires = int(time.time()) + session_days() * 86400
-    payload = str(expires).encode()
+    payload = f"{expires}:{current_epoch(conn)}".encode()
     sig = hmac.new(_secret(), payload, hashlib.sha256).digest()
     return base64.urlsafe_b64encode(payload + sig).decode()
 
 
-def token_valid(token: str) -> bool:
+def token_valid(token: str, conn=None) -> bool:
     try:
         raw = base64.urlsafe_b64decode(token.encode())
         if len(raw) <= DIGEST_SIZE:
@@ -77,7 +170,12 @@ def token_valid(token: str) -> bool:
         expected = hmac.new(_secret(), payload, hashlib.sha256).digest()
         if not hmac.compare_digest(sig, expected):
             return False
-        return int(payload) > time.time()
+        expires_s, _, epoch_s = payload.decode().partition(":")
+        if int(expires_s) <= time.time():
+            return False
+        if conn is not None and int(epoch_s or 0) != current_epoch(conn):
+            return False
+        return True
     except Exception:
         return False
 
@@ -149,10 +247,15 @@ def is_https(request: Request) -> bool:
     return request.url.scheme == "https"
 
 
-def require_auth(parts_session: str | None = Cookie(default=None)):
-    """FastAPI dependency guarding every data route."""
+def require_auth(parts_session: str | None = Cookie(default=None), conn=Depends(db.get_db)):
+    """FastAPI dependency guarding every data route.
+
+    Takes the same request-scoped connection the route uses (FastAPI caches
+    dependency results per request), so checking the session epoch costs one
+    indexed lookup rather than a second connection.
+    """
     if not auth_enabled():
         return True
-    if parts_session and token_valid(parts_session):
+    if parts_session and token_valid(parts_session, conn):
         return True
     raise HTTPException(status_code=401, detail="Not authenticated")
diff --git a/app/db.py b/app/db.py
index fc09356..81e3bb4 100644
--- a/app/db.py
+++ b/app/db.py
@@ -94,6 +94,14 @@ CREATE TABLE IF NOT EXISTS stock_log (
 );
 CREATE INDEX IF NOT EXISTS stock_log_part ON stock_log(part_id, id DESC);
 
+-- Small key/value store for things that must outlive a container rebuild and
+-- be changeable without editing a file on the host: the password hash and the
+-- session epoch live here, in the /data volume.
+CREATE TABLE IF NOT EXISTS settings (
+  key   TEXT PRIMARY KEY,
+  value TEXT NOT NULL
+);
+
 CREATE VIRTUAL TABLE IF NOT EXISTS parts_fts USING fts5(
   name, description, manufacturer, mpn, specs, tags, category, location,
   tokenize='unicode61 remove_diacritics 2'
@@ -131,6 +139,19 @@ def init():
         _initialised = True
 
 
+def get_setting(conn, key: str, default: str | None = None) -> str | None:
+    row = conn.execute("SELECT value FROM settings WHERE key = ?", (key,)).fetchone()
+    return row["value"] if row else default
+
+
+def set_setting(conn, key: str, value: str):
+    conn.execute(
+        "INSERT INTO settings(key, value) VALUES (?, ?) "
+        "ON CONFLICT(key) DO UPDATE SET value = excluded.value",
+        (key, str(value)),
+    )
+
+
 @contextmanager
 def session():
     conn = connect()
diff --git a/app/main.py b/app/main.py
index cfcfc7d..c4f72d3 100644
--- a/app/main.py
+++ b/app/main.py
@@ -9,12 +9,14 @@ consumer of the same endpoints rather than a fork of them.
 import asyncio
 import hashlib
 import json
+import math
 import os
 import sqlite3
 from contextlib import asynccontextmanager
 from typing import Annotated, Any, Literal
 
 from fastapi import Depends, FastAPI, HTTPException, Query, Request, Response
+from fastapi.exceptions import RequestValidationError
 from fastapi.responses import HTMLResponse, JSONResponse
 from fastapi.staticfiles import StaticFiles
 from pydantic import AfterValidator, BaseModel, Field
@@ -69,10 +71,10 @@ class PartIn(BaseModel):
     location_id: int | None = None
     manufacturer: Text = Field(default="", max_length=200)
     mpn: Text = Field(default="", max_length=120)
-    quantity: float = Field(default=0, ge=0)
+    quantity: float = Field(default=0, ge=0, allow_inf_nan=False)
     unit: RequiredText = Field(default="pcs", max_length=20)
-    min_quantity: float | None = Field(default=None, ge=0)
-    cost_each: float | None = Field(default=None, ge=0)
+    min_quantity: float | None = Field(default=None, ge=0, allow_inf_nan=False)
+    cost_each: float | None = Field(default=None, ge=0, allow_inf_nan=False)
     datasheet_url: Text = Field(default="", max_length=1000)
     product_url: Text = Field(default="", max_length=1000)
     notes: Text = Field(default="", max_length=4000)
@@ -87,10 +89,10 @@ class PartPatch(BaseModel):
     location_id: int | None = None
     manufacturer: Text | None = Field(default=None, max_length=200)
     mpn: Text | None = Field(default=None, max_length=120)
-    quantity: float | None = Field(default=None, ge=0)
+    quantity: float | None = Field(default=None, ge=0, allow_inf_nan=False)
     unit: RequiredText | None = Field(default=None, max_length=20)
-    min_quantity: float | None = Field(default=None, ge=0)
-    cost_each: float | None = Field(default=None, ge=0)
+    min_quantity: float | None = Field(default=None, ge=0, allow_inf_nan=False)
+    cost_each: float | None = Field(default=None, ge=0, allow_inf_nan=False)
     datasheet_url: Text | None = Field(default=None, max_length=1000)
     product_url: Text | None = Field(default=None, max_length=1000)
     notes: Text | None = Field(default=None, max_length=4000)
@@ -109,7 +111,7 @@ PART_COLUMNS = [
 
 
 class AdjustIn(BaseModel):
-    delta: float
+    delta: float = Field(allow_inf_nan=False)
     reason: Text = Field(default="", max_length=300)
 
 
@@ -126,6 +128,11 @@ class LoginIn(BaseModel):
     password: str = Field(max_length=500)
 
 
+class PasswordChangeIn(BaseModel):
+    current_password: str = Field(max_length=500)
+    new_password: str = Field(max_length=500)
+
+
 # --- helpers ----------------------------------------------------------------
 
 def _specs_for(conn, part_ids: list[int]) -> dict[int, list[dict]]:
@@ -240,6 +247,32 @@ def _check_parent(conn, table: str, node_id: int, parent_id: int | None, label:
         raise HTTPException(400, f"A {label} cannot be moved beneath itself")
 
 
+# --- error handling ---------------------------------------------------------
+
+def _json_safe(value):
+    """Make a validation-error payload encodable.
+
+    FastAPI echoes the rejected value back in the error detail. When that value
+    is Infinity or NaN — the very thing being rejected — the JSON encoder
+    refuses it and a clean 422 turns into a serialisation failure. Stringify
+    anything the encoder can't represent.
+    """
+    if isinstance(value, float):
+        return value if math.isfinite(value) else str(value)
+    if isinstance(value, dict):
+        return {str(k): _json_safe(v) for k, v in value.items()}
+    if isinstance(value, (list, tuple, set)):
+        return [_json_safe(v) for v in value]
+    if isinstance(value, (str, int, bool)) or value is None:
+        return value
+    return str(value)
+
+
+@app.exception_handler(RequestValidationError)
+def validation_error(request: Request, exc: RequestValidationError):
+    return JSONResponse({"detail": _json_safe(exc.errors())}, status_code=422)
+
+
 # --- middleware -------------------------------------------------------------
 
 @app.middleware("http")
@@ -268,19 +301,35 @@ async def security_headers(request: Request, call_next):
 
 # --- auth routes ------------------------------------------------------------
 
+def _set_session_cookie(response: Response, request: Request, conn):
+    response.set_cookie(
+        auth.COOKIE_NAME,
+        auth.issue_token(conn),
+        max_age=auth.session_days() * 86400,
+        httponly=True,
+        samesite="lax",
+        secure=auth.is_https(request),
+        path="/",
+    )
+
+
 @app.get("/api/me")
-def me(request: Request):
+def me(request: Request, conn=Depends(db.get_db)):
     if not auth.auth_enabled():
-        return {"authenticated": True, "auth_required": False}
+        return {"authenticated": True, "auth_required": False, "using_bootstrap_password": False}
     token = request.cookies.get(auth.COOKIE_NAME)
+    authenticated = bool(token and auth.token_valid(token, conn))
     return {
-        "authenticated": bool(token and auth.token_valid(token)),
+        "authenticated": authenticated,
         "auth_required": True,
+        # Surfaced so the UI can nag until the handed-over password is replaced.
+        "using_bootstrap_password": authenticated and auth.using_bootstrap_password(conn),
+        "min_password_length": auth.MIN_PASSWORD_LENGTH,
     }
 
 
 @app.post("/api/login")
-async def login(body: LoginIn, response: Response, request: Request):
+async def login(body: LoginIn, response: Response, request: Request, conn=Depends(db.get_db)):
     if not auth.auth_enabled():
         return {"authenticated": True, "auth_required": False}
 
@@ -290,7 +339,7 @@ async def login(body: LoginIn, response: Response, request: Request):
             429, "Too many failed attempts", headers={"Retry-After": str(retry_after)}
         )
 
-    if not auth.check_password(body.password):
+    if not auth.check_password(conn, body.password):
         auth.record_failure()
         # Async sleep, so a burst of guesses can't tie up the worker threadpool
         # that real requests need.
@@ -298,16 +347,52 @@ async def login(body: LoginIn, response: Response, request: Request):
         raise HTTPException(401, "Incorrect password")
 
     auth.clear_failures()
-    response.set_cookie(
-        auth.COOKIE_NAME,
-        auth.issue_token(),
-        max_age=auth.session_days() * 86400,
-        httponly=True,
-        samesite="lax",
-        secure=auth.is_https(request),
-        path="/",
-    )
-    return {"authenticated": True, "auth_required": True}
+    _set_session_cookie(response, request, conn)
+    return {
+        "authenticated": True,
+        "auth_required": True,
+        "using_bootstrap_password": auth.using_bootstrap_password(conn),
+    }
+
+
+@app.post("/api/password", dependencies=[Depends(auth.require_auth)])
+async def change_password(
+    body: PasswordChangeIn, response: Response, request: Request, conn=Depends(db.get_db)
+):
+    """Change the password from inside the app.
+
+    Requires the current password even though the caller already holds a valid
+    session: a borrowed browser tab should not be enough to lock the owner out.
+    """
+    if not auth.auth_enabled():
+        raise HTTPException(400, "Authentication is disabled, so there is no password to change")
+
+    if not auth.check_password(conn, body.current_password):
+        auth.record_failure()
+        await asyncio.sleep(0.5)
+        raise HTTPException(403, "Current password is incorrect")
+
+    problem = auth.password_problem(body.new_password)
+    if problem:
+        raise HTTPException(422, problem)
+    if body.new_password == body.current_password:
+        raise HTTPException(422, "New password must be different from the current one")
+
+    auth.clear_failures()
+    # Bumps the session epoch, so every cookie issued before now stops working.
+    auth.set_password(conn, body.new_password)
+    # Re-issue for the caller, so changing the password doesn't log you out of
+    # the tab you changed it in.
+    _set_session_cookie(response, request, conn)
+    return {"changed": True, "other_sessions_signed_out": True}
+
+
+@app.post("/api/sessions/revoke", dependencies=[Depends(auth.require_auth)])
+def revoke_sessions(response: Response, request: Request, conn=Depends(db.get_db)):
+    """Sign out every other device, keeping this one signed in."""
+    auth.bump_epoch(conn)
+    _set_session_cookie(response, request, conn)
+    return {"revoked": True}
 
 
 @app.post("/api/logout")
@@ -503,6 +588,8 @@ def adjust_part(part_id: int, body: AdjustIn, conn=Depends(db.get_db)):
 
 @app.get("/api/parts/{part_id}/history", dependencies=[Depends(auth.require_auth)])
 def part_history(part_id: int, conn=Depends(db.get_db), limit: int = Query(default=50, ge=1, le=500)):
+    if conn.execute("SELECT 1 FROM parts WHERE id = ?", (part_id,)).fetchone() is None:
+        raise HTTPException(404, "Part not found")
     rows = conn.execute(
         "SELECT * FROM stock_log WHERE part_id = ? ORDER BY id DESC LIMIT ?", (part_id, limit)
     ).fetchall()
@@ -578,6 +665,10 @@ def create_category(body: NodeIn, conn=Depends(db.get_db)):
 
 @app.patch("/api/categories/{cat_id}", dependencies=[Depends(auth.require_auth)])
 def update_category(cat_id: int, body: NodeIn, conn=Depends(db.get_db)):
+    # Before the first read: the affected-parts scan and the reindex that
+    # follows it have to see one consistent tree, or a concurrent write can slip
+    # between them and leave the search index describing the old taxonomy.
+    db.begin_immediate(conn)
     _require_node(conn, "categories", cat_id, "Category")
     _check_parent(conn, "categories", cat_id, body.parent_id, "category")
     affected = db.parts_under(conn, "categories", cat_id)
@@ -596,6 +687,10 @@ def update_category(cat_id: int, body: NodeIn, conn=Depends(db.get_db)):
 
 @app.delete("/api/categories/{cat_id}", dependencies=[Depends(auth.require_auth)])
 def delete_category(cat_id: int, conn=Depends(db.get_db)):
+    # Before the first read: the affected-parts scan and the reindex that
+    # follows it have to see one consistent tree, or a concurrent write can slip
+    # between them and leave the search index describing the old taxonomy.
+    db.begin_immediate(conn)
     _require_node(conn, "categories", cat_id, "Category")
     # Capture the parts first: ON DELETE SET NULL means they survive as
     # uncategorised rather than vanish, but their indexed path must be rebuilt.
@@ -626,6 +721,10 @@ def create_location(body: NodeIn, conn=Depends(db.get_db)):
 
 @app.patch("/api/locations/{loc_id}", dependencies=[Depends(auth.require_auth)])
 def update_location(loc_id: int, body: NodeIn, conn=Depends(db.get_db)):
+    # Before the first read: the affected-parts scan and the reindex that
+    # follows it have to see one consistent tree, or a concurrent write can slip
+    # between them and leave the search index describing the old taxonomy.
+    db.begin_immediate(conn)
     _require_node(conn, "locations", loc_id, "Location")
     _check_parent(conn, "locations", loc_id, body.parent_id, "location")
     affected = db.parts_under(conn, "locations", loc_id)
@@ -642,6 +741,10 @@ def update_location(loc_id: int, body: NodeIn, conn=Depends(db.get_db)):
 
 @app.delete("/api/locations/{loc_id}", dependencies=[Depends(auth.require_auth)])
 def delete_location(loc_id: int, conn=Depends(db.get_db)):
+    # Before the first read: the affected-parts scan and the reindex that
+    # follows it have to see one consistent tree, or a concurrent write can slip
+    # between them and leave the search index describing the old taxonomy.
+    db.begin_immediate(conn)
     _require_node(conn, "locations", loc_id, "Location")
     affected = db.parts_under(conn, "locations", loc_id)
     conn.execute("DELETE FROM locations WHERE id = ?", (loc_id,))
diff --git a/static/app.css b/static/app.css
index 3c4483a..3b26fd2 100644
--- a/static/app.css
+++ b/static/app.css
@@ -89,6 +89,21 @@ header .brand { font-weight: 700; letter-spacing: -.01em; white-space: nowrap; }
 header .search { flex: 1 1 240px; min-width: 160px; }
 header .stat { color: var(--dim); font-size: 13px; white-space: nowrap; }
 
+.banner {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  gap: 12px;
+  flex-wrap: wrap;
+  margin: 12px 16px -4px;
+  padding: 10px 14px;
+  border: 1px solid var(--warn);
+  border-radius: var(--radius);
+  background: rgba(240, 168, 72, .10);
+  color: var(--warn);
+  font-size: 14px;
+}
+
 .layout { display: flex; align-items: flex-start; gap: 18px; padding: 16px; max-width: 1400px; margin: 0 auto; }
 
 aside {
diff --git a/static/app.js b/static/app.js
index 6baee12..c607109 100644
--- a/static/app.js
+++ b/static/app.js
@@ -23,6 +23,8 @@ const state = {
   locations: [],
   tags: [],
   authRequired: true,
+  usingBootstrap: false,
+  minPasswordLength: 8,
 };
 
 // --- plumbing ---------------------------------------------------------------
@@ -70,6 +72,7 @@ function showApp() {
   $("#login").classList.add("hidden");
   $("#app").classList.remove("hidden");
   $("#logout-btn").classList.toggle("hidden", !state.authRequired);
+  $("#bootstrap-banner").classList.toggle("hidden", !state.usingBootstrap);
 }
 
 $("#login-form").addEventListener("submit", async (e) => {
@@ -77,8 +80,9 @@ $("#login-form").addEventListener("submit", async (e) => {
   const err = $("#login-error");
   err.classList.add("hidden");
   try {
-    await api("/api/login", { method: "POST", body: { password: $("#password").value } });
+    const session = await api("/api/login", { method: "POST", body: { password: $("#password").value } });
     $("#password").value = "";
+    state.usingBootstrap = !!session.using_bootstrap_password;
     showApp();
     await boot();
   } catch (ex) {
@@ -493,13 +497,36 @@ function openPartModal(part) {
 
 // --- manage categories / locations ------------------------------------------
 
-function openManageModal() {
+function openManageModal(focusPassword = false) {
   const overlay = openModal(`
     <header>
-      <strong>Categories &amp; locations</strong>
+      <strong>Settings</strong>
       <button class="ghost small" data-close>✕</button>
     </header>
     <div class="content">
+      ${state.authRequired ? `
+      <section id="password-section" style="margin-bottom:24px">
+        <label>Password</label>
+        ${state.usingBootstrap
+          ? '<p style="color:var(--warn);font-size:13px;margin:0 0 10px">You\'re still using the password you were handed. Setting your own here also signs out every other device.</p>'
+          : '<p style="color:var(--dim);font-size:13px;margin:0 0 10px">Changing your password signs out every other device.</p>'}
+        <div class="grid">
+          <div class="full">
+            <input id="pw-current" type="password" autocomplete="current-password" placeholder="Current password">
+          </div>
+          <div>
+            <input id="pw-new" type="password" autocomplete="new-password" placeholder="New password">
+          </div>
+          <div>
+            <input id="pw-confirm" type="password" autocomplete="new-password" placeholder="Repeat new password">
+          </div>
+        </div>
+        <div style="display:flex;gap:10px;align-items:center;margin-top:10px;flex-wrap:wrap">
+          <button class="small primary" id="pw-save">Change password</button>
+          <button class="small ghost" id="pw-revoke" title="Keeps this device signed in">Sign out other devices</button>
+          <span id="pw-msg" style="font-size:13px"></span>
+        </div>
+      </section>` : ""}
       <div class="grid">
         <div>
           <label>New category</label>
@@ -530,6 +557,50 @@ function openManageModal() {
 
   overlay.querySelectorAll("[data-close]").forEach((b) => (b.onclick = closeModal));
 
+  const pwSave = overlay.querySelector("#pw-save");
+  if (pwSave) {
+    const msg = overlay.querySelector("#pw-msg");
+    const say = (text, bad) => {
+      msg.textContent = text;
+      msg.style.color = bad ? "var(--bad)" : "var(--good)";
+    };
+    pwSave.onclick = async () => {
+      const current = overlay.querySelector("#pw-current").value;
+      const next = overlay.querySelector("#pw-new").value;
+      const confirmed = overlay.querySelector("#pw-confirm").value;
+      if (!current) return say("Enter your current password", true);
+      if (next !== confirmed) return say("New passwords don't match", true);
+      if (next.length < state.minPasswordLength)
+        return say(`At least ${state.minPasswordLength} characters`, true);
+      pwSave.disabled = true;
+      try {
+        await api("/api/password", {
+          method: "POST",
+          body: { current_password: current, new_password: next },
+        });
+        overlay.querySelectorAll("#pw-current, #pw-new, #pw-confirm").forEach((i) => (i.value = ""));
+        state.usingBootstrap = false;
+        $("#bootstrap-banner").classList.add("hidden");
+        say("Password changed. Other devices signed out.", false);
+        toast("Password changed");
+      } catch (ex) {
+        say(ex.message, true);
+      } finally {
+        pwSave.disabled = false;
+      }
+    };
+    overlay.querySelector("#pw-revoke").onclick = async () => {
+      if (!confirm("Sign out every other device? This one stays signed in.")) return;
+      try {
+        await api("/api/sessions/revoke", { method: "POST" });
+        say("Other devices signed out.", false);
+      } catch (ex) {
+        say(ex.message, true);
+      }
+    };
+    if (focusPassword) setTimeout(() => overlay.querySelector("#pw-current").focus(), 50);
+  }
+
   const renderRows = () => {
     const draw = (items, box, kind) => {
       box.innerHTML = "";
@@ -645,7 +716,8 @@ $("#sort").addEventListener("change", (e) => {
 
 $("#filters-btn").onclick = () => setSidebar(!$("#sidebar").classList.contains("open"));
 $("#add-btn").onclick = () => openPartModal(null);
-$("#manage-btn").onclick = openManageModal;
+$("#manage-btn").onclick = () => openManageModal(false);
+$("#banner-change").onclick = () => openManageModal(true);
 $("#more-btn").onclick = () => search(true);
 
 $("#filter-all").onclick = () => {
@@ -669,6 +741,8 @@ async function boot() {
   try {
     const me = await api("/api/me");
     state.authRequired = me.auth_required;
+    state.usingBootstrap = !!me.using_bootstrap_password;
+    state.minPasswordLength = me.min_password_length || state.minPasswordLength;
     if (!me.authenticated) return showLogin();
     showApp();
     await boot();
diff --git a/static/index.html b/static/index.html
index 3b92681..3726287 100644
--- a/static/index.html
+++ b/static/index.html
@@ -27,10 +27,15 @@
     <span class="stat" id="stats"></span>
     <button class="ghost small mobile-only" id="filters-btn">Filters</button>
     <button class="primary" id="add-btn">+ Add</button>
-    <button class="ghost small" id="manage-btn" title="Categories &amp; locations">⚙</button>
+    <button class="ghost small" id="manage-btn" title="Settings">⚙</button>
     <button class="ghost small hidden" id="logout-btn" title="Log out">⏻</button>
   </header>
 
+  <div id="bootstrap-banner" class="banner hidden">
+    <span>You're still using the password that was handed to you. Set your own.</span>
+    <button class="small primary" id="banner-change">Change password</button>
+  </div>
+
   <div class="layout">
     <aside id="sidebar">
       <h3>Filters</h3>
diff --git a/tests/test_api.py b/tests/test_api.py
index fc389ea..ae0c5b1 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -27,8 +27,8 @@ with TestClient(app) as client:
     import app.auth as _auth
     import base64 as _b64, hashlib as _hl, hmac as _hm
 
-    def _issue_at(exp):
-        payload = str(exp).encode()
+    def _issue_at(exp, epoch=0):
+        payload = f"{exp}:{epoch}".encode()
         return _b64.urlsafe_b64encode(
             payload + _hm.new(_auth._secret(), payload, _hl.sha256).digest()).decode()
 
@@ -198,13 +198,52 @@ with TestClient(app) as client:
     check("deleted part is gone", client.get(f"/api/parts/{screw['id']}").status_code == 404)
     check("deleted part leaves the index", "M3x8 socket cap screw" not in ids("M3x8"))
     check("missing part 404s", client.get("/api/parts/999999").status_code == 404)
+    check("history of a missing part 404s",
+          client.get("/api/parts/999999/history").status_code == 404)
+    # httpx refuses to serialise inf/nan, so these go as raw bodies — which is
+    # exactly how a real client would smuggle them in: Python's json.loads
+    # accepts the bare `Infinity` and `NaN` tokens.
+    JSONH = {"Content-Type": "application/json"}
+
+    def raw_post(path, body):
+        return client.post(path, content=body, headers=JSONH)
+
+    def raw_patch(path, body):
+        return client.patch(path, content=body, headers=JSONH)
+
+    check("Infinity quantity rejected",
+          raw_post("/api/parts", '{"name":"inf","quantity":Infinity}').status_code == 422)
+    check("-Infinity quantity rejected",
+          raw_post("/api/parts", '{"name":"ninf","quantity":-Infinity}').status_code == 422)
+    check("NaN quantity rejected",
+          raw_post("/api/parts", '{"name":"nan","quantity":NaN}').status_code == 422)
+    check("Infinity cost rejected",
+          raw_post("/api/parts", '{"name":"inf2","cost_each":Infinity}').status_code == 422)
+    check("Infinity min_quantity rejected",
+          raw_post("/api/parts", '{"name":"inf3","min_quantity":Infinity}').status_code == 422)
+    _infp = client.post("/api/parts", json={"name": "inf target", "quantity": 5}).json()["id"]
+    check("Infinity adjustment delta rejected",
+          raw_post(f"/api/parts/{_infp}/adjust", '{"delta":Infinity}').status_code == 422)
+    check("NaN adjustment delta rejected",
+          raw_post(f"/api/parts/{_infp}/adjust", '{"delta":NaN}').status_code == 422)
+    check("Infinity PATCH quantity rejected",
+          raw_patch(f"/api/parts/{_infp}", '{"quantity":Infinity}').status_code == 422)
+    check("the part is untouched after a rejected Infinity",
+          client.get(f"/api/parts/{_infp}").json()["quantity"] == 5)
     check("adjusting a missing part 404s",
           client.post("/api/parts/999999/adjust", json={"delta": 1}).status_code == 404)
 
     # --- stats & validation ---
+    # Derived from the listing rather than a magic number, so adding a fixture
+    # part earlier in the file can't silently invalidate it.
     s = client.get("/api/stats").json()
-    check("stats counts remaining parts", s["parts"] == 2, str(s))
-    check("stats counts low stock", s["low_stock"] == 2, str(s))
+    listed = client.get("/api/parts", params={"limit": 1000}).json()
+    check("stats part count matches the listing", s["parts"] == listed["total"], str(s))
+    check("stats low-stock count matches the listing",
+          s["low_stock"] == sum(1 for p in listed["items"] if p["low_stock"]), str(s))
+    check("stats value matches the listing",
+          s["estimated_value"] == round(sum(p["quantity"] * (p["cost_each"] or 0)
+                                            for p in listed["items"]), 2), str(s))
     check("whitespace-only name rejected",
           client.post("/api/parts", json={"name": "  "}).status_code == 422)
     check("negative quantity rejected",
@@ -351,6 +390,83 @@ with TestClient(app) as client:
           client.post("/api/login", json={"password": "hunter2"}).status_code == 200)
     check("a successful login resets the failure budget", auth_mod.login_retry_after() == 0)
 
+    # --- password management through the API ---
+    check("bootstrap password is flagged", client.get("/api/me").json()["using_bootstrap_password"] is True)
+    check("min length is advertised", client.get("/api/me").json()["min_password_length"] == 8)
+
+    check("wrong current password is refused",
+          client.post("/api/password",
+                      json={"current_password": "nope", "new_password": "brand-new-secret"}).status_code == 403)
+    auth_mod.clear_failures()
+    check("short new password rejected",
+          client.post("/api/password",
+                      json={"current_password": "hunter2", "new_password": "short"}).status_code == 422)
+    check("reusing the current password rejected",
+          client.post("/api/password",
+                      json={"current_password": "hunter2", "new_password": "hunter2"}).status_code == 422)
+    check("still logged in after failed attempts", client.get("/api/parts").status_code == 200)
+
+    # A second, independent session that should be cut off by the change.
+    other = TestClient(app)
+    other.post("/api/login", json={"password": "hunter2"})
+    check("second session works before the change", other.get("/api/parts").status_code == 200)
+
+    r = client.post("/api/password",
+                    json={"current_password": "hunter2", "new_password": "correct-horse-battery"})
+    check("password change succeeds", r.status_code == 200, r.text)
+    check("change reports other sessions signed out", r.json()["other_sessions_signed_out"] is True)
+    check("the changing session stays signed in", client.get("/api/parts").status_code == 200)
+    check("other sessions are signed out", other.get("/api/parts").status_code == 401)
+    check("bootstrap flag clears", client.get("/api/me").json()["using_bootstrap_password"] is False)
+
+    fresh = TestClient(app)
+    check("the old password no longer works",
+          fresh.post("/api/login", json={"password": "hunter2"}).status_code == 401)
+    auth_mod.clear_failures()
+    check("the bootstrap env password is ignored once one is set",
+          fresh.post("/api/login", json={"password": os.environ["PARTS_PASSWORD"]}).status_code == 401)
+    auth_mod.clear_failures()
+    check("the new password works",
+          fresh.post("/api/login", json={"password": "correct-horse-battery"}).status_code == 200)
+    check("the new session can read data", fresh.get("/api/parts").status_code == 200)
+
+    # --- sign out other devices, without signing out this one ---
+    third = TestClient(app)
+    third.post("/api/login", json={"password": "correct-horse-battery"})
+    check("third session works", third.get("/api/parts").status_code == 200)
+    check("revoke succeeds", client.post("/api/sessions/revoke").status_code == 200)
+    check("revoke keeps the calling session", client.get("/api/parts").status_code == 200)
+    check("revoke cuts off the other session", third.get("/api/parts").status_code == 401)
+
+    # --- the hash itself ---
+    import app.db as _db
+    with _db.session() as _conn:
+        stored = auth_mod.stored_hash(_conn)
+    check("password is stored hashed, not in the clear",
+          stored is not None and stored.startswith("scrypt$") and "correct-horse-battery" not in stored)
+    check("the stored hash verifies", auth_mod.verify_hash("correct-horse-battery", stored))
+    check("the stored hash rejects a wrong password", not auth_mod.verify_hash("wrong", stored))
+    check("two hashes of the same password differ (salted)",
+          auth_mod.hash_password("same") != auth_mod.hash_password("same"))
+
+    # --- recovery CLI ---
+    import app.admin as _admin
+    check("admin set-password works", _admin.main(["set-password", "cli-set-password"]) == 0)
+    cli = TestClient(app)
+    check("CLI-set password logs in",
+          cli.post("/api/login", json={"password": "cli-set-password"}).status_code == 200)
+    auth_mod.clear_failures()
+    check("CLI change signed out the API session", client.get("/api/parts").status_code == 401)
+    check("admin rejects a short password", _admin.main(["set-password", "abc"]) == 1)
+    check("admin show-status works", _admin.main(["show-status"]) == 0)
+    check("admin rejects an unknown command", _admin.main(["nonsense"]) == 2)
+    check("admin clear-password works", _admin.main(["clear-password"]) == 0)
+    back = TestClient(app)
+    check("clearing restores the env password",
+          back.post("/api/login", json={"password": os.environ["PARTS_PASSWORD"]}).status_code == 200)
+    check("bootstrap flag returns after clearing",
+          back.get("/api/me").json()["using_bootstrap_password"] is True)
+
 print()
 if failures:
     print(f"{len(failures)} FAILED: " + "; ".join(failures))
diff --git a/tests/test_concurrency.py b/tests/test_concurrency.py
index bacfd82..07cd934 100644
--- a/tests/test_concurrency.py
+++ b/tests/test_concurrency.py
@@ -107,6 +107,49 @@ def main():
         check("PATCH log's final quantity_after matches stored",
               h3[0]["quantity_after"] == stored, f"log={h3[0]['quantity_after']} stored={stored}")
 
+        # --- taxonomy renames must leave the index agreeing with the tree ---
+        # The scan for affected parts and the reindex that follows have to see
+        # one consistent tree. Without the write lock a concurrent rename slips
+        # between them, and search keeps matching a name the UI no longer shows.
+        # Names are chosen so no token is a prefix of another: search uses prefix
+        # matching, so "Taxo 1" would legitimately match "Taxo 19" and the test
+        # would report a race that isn't there.
+        WORDS = ["alfa", "bravo", "charlie", "delta", "echo", "foxtrot", "golf",
+                 "hotel", "india", "juliett", "kilo", "lima", "mike", "november",
+                 "oscar", "papa", "quebec", "romeo", "sierra", "tango"]
+        cat = req("/api/categories", "POST", {"name": "Taxo zulu"})["id"]
+        req("/api/parts", "POST", {"name": "taxo widget", "category_id": cat, "quantity": 1})
+        names = [f"Taxo {w}" for w in WORDS]
+        with ThreadPoolExecutor(max_workers=20) as ex:
+            list(ex.map(lambda n: req(f"/api/categories/{cat}", "PATCH", {"name": n}), names))
+        final = [c["name"] for c in req("/api/categories")["items"] if c["id"] == cat][0]
+        hits_final = req(f"/api/parts?q={final.replace(' ', '+')}")["total"]
+        check("search matches the category's final name", hits_final == 1, f"{final} -> {hits_final}")
+        stale = [n for n in ["Taxo zulu"] + names if n != final
+                 and req(f"/api/parts?q={n.replace(' ', '+')}")["total"] > 0]
+        check("no superseded category name still matches", not stale, f"stale: {stale}")
+
+        # Same race with a location, and with parts being created concurrently.
+        loc = req("/api/locations", "POST", {"name": "Loc zulu"})["id"]
+        loc_names = [f"Loc {w}" for w in WORDS[:15]]
+
+        def rename_or_add(i):
+            if i % 3 == 0:
+                req("/api/parts", "POST", {"name": f"loc widget {i}", "location_id": loc, "quantity": 1})
+            else:
+                req(f"/api/locations/{loc}", "PATCH", {"name": loc_names[i % len(loc_names)]})
+
+        with ThreadPoolExecutor(max_workers=15) as ex:
+            list(ex.map(rename_or_add, range(15)))
+        final_loc = [l["name"] for l in req("/api/locations")["items"] if l["id"] == loc][0]
+        in_loc = req(f"/api/parts?location_id={loc}&limit=100")["total"]
+        by_name = req(f"/api/parts?q={final_loc.replace(' ', '+')}&limit=100")["total"]
+        check("every part in the location is indexed under its final name",
+              by_name == in_loc, f"filter={in_loc} search={by_name}")
+        stale_loc = [n for n in ["Loc zulu"] + loc_names if n != final_loc
+                     and req(f"/api/parts?q={n.replace(' ', '+')}&limit=100")["total"] > 0]
+        check("no superseded location name still matches", not stale_loc, f"stale: {stale_loc}")
+
         # --- concurrent creates don't collide ---
         with ThreadPoolExecutor(max_workers=25) as ex:
             ids = list(ex.map(