diff --git a/BUGS.md b/BUGS.md
index ed2b963..d4cdf42 100644
--- a/BUGS.md
+++ b/BUGS.md
@@ -1,11 +1,11 @@
 # Known bugs
 
 A second full-codebase audit on 2026-07-27 found **25 further issues** (4 critical, 6 high,
-7 medium, 8 low), listed below as B-43 … B-49. B-25 through B-42 are fixed (see "Previously
-fixed" below) — no Critical-, High- or Medium-severity finding remains open; the remaining 7 are
+7 medium, 8 low), listed below as B-44 … B-49. B-25 through B-43 are fixed (see "Previously
+fixed" below) — no Critical-, High- or Medium-severity finding remains open; the remaining 6 are
 Low/hygiene. The 139-test suite was green at the time of the audit, so none of these were caught
-by existing coverage — every fix lands with a regression test (the eighteen fixes so far brought
-the suite from 139 to 224).
+by existing coverage — every fix lands with a regression test (the nineteen fixes so far brought
+the suite from 139 to 230).
 
 The recurring pattern across the open findings is worth stating once: the code is rigorous
 about the failure modes that have actually been hit, and silent about the ones that have not.
@@ -18,15 +18,6 @@ admin auth, single-process assumptions, no user-facing history, etc.) are docume
 
 ## Low / hygiene
 
-### B-43 — No HTTP security headers
-
-The [Caddyfile](Caddyfile) sets no CSP, no `X-Frame-Options`/`frame-ancestors`, and no HSTS
-(Caddy does not add it on its own). The JWT lives in `localStorage`, so any XSS exfiltrates
-it, and the page is iframeable.
-**Fix:** a `header` block in the Caddyfile with `Strict-Transport-Security`,
-`X-Content-Type-Options: nosniff`, `Referrer-Policy` and a CSP tight enough for two static
-pages with no external assets (`default-src 'self'`).
-
 ### B-44 — README and CLAUDE.md contradict each other
 
 The README says to run `uvicorn --reload` directly and
@@ -83,6 +74,7 @@ already does.
 - **B-30** — a lost scripthash subscription meant a user's deposits were never credited, with no periodic safety net
 - **B-31** — resubscribing on reconnect ran serially before anything else started, freezing the chain tip (and so an in-flight draw) for the whole sweep
 - **B-42** — Swagger/ReDoc/the raw OpenAPI JSON enumerated the entire API surface, admin endpoints included, to anyone who requested them; now off by default and gated behind `ENABLE_API_DOCS`
+- **B-43** — the Caddyfile sent no CSP, no `X-Frame-Options`/`frame-ancestors`, and no HSTS, on a page whose JWT lives in `localStorage`
 - **B-32** — an RBF bump could retry forever below BIP125's relay-mandated minimum fee delta, with no ceiling on the fee rate either
 - **B-33** — `POST /auth/login` had no rate limiting, so a password could be brute-forced against an enumerable username list
 - **B-34** — password change/reset didn't invalidate already-issued JWTs, so a stolen token survived a change meant to lock it out
@@ -95,7 +87,7 @@ already does.
 - **B-41** — confirmation/reconciliation depended on a verbose `blockchain.transaction.get` reply many Electrum servers reject, and abandonment relied on fragile substring-matching of an error message
 
 See git history for the fix-by-fix breakdown (commits `f13f685`, `50a43ae`, `933760e`, and the
-B-28/B-29/B-30/B-31/B-32/B-33/B-34/B-35/B-36/B-37/B-38/B-39/B-40/B-41/B-42 fixes). Suite grew from 139 to 224 tests over the eighteen.
+B-28/B-29/B-30/B-31/B-32/B-33/B-34/B-35/B-36/B-37/B-38/B-39/B-40/B-41/B-42/B-43 fixes). Suite grew from 139 to 230 tests over the nineteen.
 
 A full-codebase audit on 2026-07-26 (commit `d4e0974`) found 24 bugs across every Python
 module under `app/`, both static frontends, and the Docker/Caddy deployment — 5 critical,
diff --git a/CLAUDE.md b/CLAUDE.md
index b916550..2a66989 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -12,7 +12,7 @@ All 10 stages of the original build order are code-complete and unit-tested —
 
 Verified on mainnet with real money: registration + address derivation, deposit crediting (1-conf), a real 10 PLM bet (broadcast → confirmed → change credited back), and one full round cycle (close → draw on a real block hash → 70/30 payout with sat math checked against the broadcast tx → confirmation → close → next round auto-opened). **Withdrawal and the RBF bump path have never been exercised against a live broadcast** — unit-tested only.
 
-**Read [BUGS.md](BUGS.md) before trusting any behaviour here.** Two audits: 2026-07-26 found 24 bugs (5 critical), all fixed; 2026-07-27 found 25 more (B-25 … B-49), of which **7 are still open** — no Critical, High or Medium remains, only Low/hygiene: an admin list endpoint with no pagination bound (B-45), unbounded `String` columns for large text (B-47), among others. BUGS.md is the live open list with a proposed fix per finding; "Known gaps" at the end of this file is for limitations accepted **by design** instead. Don't fix a BUGS.md item silently as a side effect of other work — each fix lands with its own regression test.
+**Read [BUGS.md](BUGS.md) before trusting any behaviour here.** Two audits: 2026-07-26 found 24 bugs (5 critical), all fixed; 2026-07-27 found 25 more (B-25 … B-49), of which **6 are still open** — no Critical, High or Medium remains, only Low/hygiene: an admin list endpoint with no pagination bound (B-45), unbounded `String` columns for large text (B-47), among others. BUGS.md is the live open list with a proposed fix per finding; "Known gaps" at the end of this file is for limitations accepted **by design** instead. Don't fix a BUGS.md item silently as a side effect of other work — each fix lands with its own regression test.
 
 Before writing code, read the "Architecture" section below in full plus the diagrams in [flowchart/](flowchart/): [platform-overview.mmd](flowchart/platform-overview.mmd) (the 5-phase flow) and [round-lifecycle.mmd](flowchart/round-lifecycle.mmd) (the round/draw lifecycle). Every node **and edge label** (conditions, retries, loops) is a behaviour that must be implemented as described. Regenerate the companion PDFs with `flowchart/render-pdf.sh <file>.mmd` after editing either.
 
@@ -55,7 +55,7 @@ docker compose down
 
 `SITE_ADDRESS` unset → `localhost`, Caddy issues a self-signed cert from its internal CA (browser warning on first visit is expected; `curl -k`). `SITE_ADDRESS=lottery.example.com docker compose up -d` → real Let's Encrypt cert, automatically renewed (needs DNS pointing here and ports 80+443 reachable).
 
-The `Caddyfile` sets **no** security headers — no CSP, HSTS or `X-Frame-Options` (B-43). `restart: unless-stopped` on `app` means a mid-round crash auto-restarts: `closing` and `paying_out` resume on their own, `drawing` does not (see Known gaps).
+The `Caddyfile` sends baseline security headers — HSTS, `X-Content-Type-Options: nosniff`, `X-Frame-Options: DENY`, `Referrer-Policy`, and a CSP scoped to `default-src 'self'` plus the Google Fonts `@import` in `style.css`/`admin.css`. `script-src`/`style-src` need `'unsafe-inline'` because both SPAs use inline `onclick` handlers and `style=""` attributes throughout — removing those is a separate, larger refactor, not a header change. `restart: unless-stopped` on `app` means a mid-round crash auto-restarts: `closing` and `paying_out` resume on their own, `drawing` does not (see Known gaps).
 
 ## Tech stack
 
@@ -233,7 +233,7 @@ Explicit design choices, not derivable from any single file — respect them:
 
 ## Known gaps / TODO
 
-Accepted **by design**. For actual bugs see [BUGS.md](BUGS.md) (7 open) — not duplicated here.
+Accepted **by design**. For actual bugs see [BUGS.md](BUGS.md) (6 open) — not duplicated here.
 
 - **`drawing` doesn't resume after a restart.** `_tick()` handles `open`, `closing` and `paying_out` (the last via `_retry_payout_if_due`); nothing re-enters `_wait_for_next_block` after a crash. That wait is unbounded by design (the draw's entropy genuinely depends on a future block) but no longer silent — past `_DRAW_STALL_THRESHOLD_SECONDS` it logs progress and writes a `draw_stalled` audit entry, and `GET /rounds/current`'s `draw_waiting_since` surfaces it live (B-36). Restart-resumption itself remains the last prerequisite for running unattended.
 - **RBF handles one shape only**: a single change output, back to the tx's own sender, big enough to absorb the increase. No extra-input fallback — an exact-amount tx or too-small change raises `RbfError`. Not permanent, though: an unbumpable tx that never confirms is eventually abandoned and its UTXOs released.
diff --git a/Caddyfile b/Caddyfile
index b51229c..f6db413 100644
--- a/Caddyfile
+++ b/Caddyfile
@@ -13,5 +13,21 @@
 		not path /rounds/stream
 	}
 	encode @not_sse gzip
+
+	# B-43: Caddy adds none of these on its own. The JWT lives in
+	# localStorage, so any XSS exfiltrates it — CSP is the main mitigation.
+	# script-src/style-src need 'unsafe-inline' because both SPAs
+	# (app/static/index.html, admin.html) use inline onclick handlers and
+	# style="" attributes throughout; removing those is a separate,
+	# larger refactor, not a header change. fonts.googleapis.com/gstatic.com
+	# are the one external asset (the Google Fonts @import in style.css/admin.css).
+	header {
+		Strict-Transport-Security "max-age=31536000; includeSubDomains"
+		X-Content-Type-Options "nosniff"
+		X-Frame-Options "DENY"
+		Referrer-Policy "strict-origin-when-cross-origin"
+		Content-Security-Policy "default-src 'self'; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; font-src 'self' https://fonts.gstatic.com; img-src 'self'; connect-src 'self'; base-uri 'self'; form-action 'self'; frame-ancestors 'none'; object-src 'none'"
+	}
+
 	reverse_proxy app:8123
 }
diff --git a/tests/unit/test_caddyfile_security_headers.py b/tests/unit/test_caddyfile_security_headers.py
new file mode 100644
index 0000000..ed12a9a
--- /dev/null
+++ b/tests/unit/test_caddyfile_security_headers.py
@@ -0,0 +1,35 @@
+"""B-43: the Caddyfile must keep sending baseline security headers. Caddy adds
+none of these on its own, and the JWT lives in localStorage, so a regression
+here silently reopens an XSS/clickjacking exposure with no test ever failing
+in the Python suite (the Caddyfile isn't imported/exercised by anything else)."""
+
+from pathlib import Path
+
+CADDYFILE = (Path(__file__).parent.parent.parent / "Caddyfile").read_text()
+
+
+def test_header_block_present():
+    assert "header {" in CADDYFILE
+
+
+def test_hsts_is_set():
+    assert "Strict-Transport-Security" in CADDYFILE
+    assert "max-age=" in CADDYFILE
+
+
+def test_nosniff_is_set():
+    assert 'X-Content-Type-Options "nosniff"' in CADDYFILE
+
+
+def test_frame_ancestors_are_blocked():
+    assert 'X-Frame-Options "DENY"' in CADDYFILE
+    assert "frame-ancestors 'none'" in CADDYFILE
+
+
+def test_referrer_policy_is_set():
+    assert "Referrer-Policy" in CADDYFILE
+
+
+def test_csp_default_src_is_self():
+    assert "Content-Security-Policy" in CADDYFILE
+    assert "default-src 'self'" in CADDYFILE