fix: add web-builder Docker stage for JSX compilation

The previous rework removed web/dist/ from git tracking (correct) but did not add a web-builder stage to the Dockerfile. This caused //go:embed dist/* in web/embed.go to fail with 'no matching files found'. Add the 4-stage Dockerfile layout: 1. web-builder: compile Preact JSX SPA via esbuild 2. lint: format checking and linting with placeholder dist files 3. builder: compile Go binaries with real web assets from web-builder 4. runtime: minimal Alpine image with neoircd binary Also update README to document the 4-stage build.
fix: move hashcash PoW from build artifact to JSX source
2026-03-10 03:09:12 -07:00 · 2026-03-10 03:09:12 -07:00 · 2026-03-10 03:09:12 -07:00
21 changed files with 680 additions and 318 deletions
--- a/.gitignore
+++ b/.gitignore
@@ -21,7 +21,6 @@ node_modules/
 *.key

 # Build artifacts
-web/dist/
 /neoircd
 /bin/
 *.exe
@@ -37,3 +36,4 @@ data.db
 debug.log
 /neoirc-cli
 web/node_modules/
+web/dist/
--- a/README.md
+++ b/README.md
@@ -987,7 +987,18 @@ the format:

 Create a new user session. This is the entry point for all clients.

-**Request:**
+If the server requires hashcash proof-of-work (see
+[Hashcash Proof-of-Work](#hashcash-proof-of-work)), the client must include a
+valid stamp in the `X-Hashcash` request header. The required difficulty is
+advertised via `GET /api/v1/server` in the `hashcash_bits` field.
+
+**Request Headers:**
+
+| Header       | Required | Description |
+|--------------|----------|-------------|
+| `X-Hashcash` | Conditional | Hashcash stamp (required when server has `hashcash_bits` > 0) |
+
+**Request Body:**
 ```json
 {"nick": "alice"}
 ```
@@ -1016,12 +1027,15 @@ Create a new user session. This is the entry point for all clients.
 | Status | Error | When |
 |--------|-------|------|
 | 400    | `nick must be 1-32 characters` | Empty or too-long nick |
+| 402    | `hashcash proof-of-work required` | Missing `X-Hashcash` header when hashcash is enabled |
+| 402    | `invalid hashcash stamp: ...` | Stamp fails validation (wrong bits, expired, reused, etc.) |
 | 409    | `nick already taken` | Another active session holds this nick |

 **curl example:**
 ```bash
 TOKEN=$(curl -s -X POST http://localhost:8080/api/v1/session \
  -H 'Content-Type: application/json' \
+  -H 'X-Hashcash: 1:20:260310:neoirc::3a2f1' \
  -d '{"nick":"alice"}' | jq -r .token)
 echo $TOKEN
 ```
@@ -1032,12 +1046,6 @@ Return the current user's session state.

 **Request:** No body. Requires auth.

-**Query Parameters:**
-
-| Parameter | Type   | Default | Description |
-|-----------|--------|---------|-------------|
-| `initChannelState` | string | (none) | When set to `1`, enqueues synthetic JOIN + TOPIC + NAMES messages for every channel the session belongs to into the calling client's queue. Used by the SPA on reconnect to restore channel tabs without re-sending JOIN commands. |
-
 **Response:** `200 OK`
 ```json
 {
@@ -1070,12 +1078,6 @@ curl -s http://localhost:8080/api/v1/state \
  -H "Authorization: Bearer $TOKEN" | jq .
 ```

-**Reconnect with channel state initialization:**
-```bash
-curl -s "http://localhost:8080/api/v1/state?initChannelState=1" \
-  -H "Authorization: Bearer $TOKEN" | jq .
-```
-
 ### GET /api/v1/messages — Poll Messages (Long-Poll)

 Retrieve messages from the client's delivery queue. This is the primary
@@ -1376,16 +1378,18 @@ Return server metadata. No authentication required.
  "name": "My NeoIRC Server",
  "version": "0.1.0",
  "motd": "Welcome! Be nice.",
-  "users": 42
+  "users": 42,
+  "hashcash_bits": 20
 }
 ```

-| Field     | Type    | Description |
-|-----------|---------|-------------|
-| `name`    | string  | Server display name |
-| `version` | string  | Server version |
-| `motd`    | string  | Message of the day |
-| `users`   | integer | Number of currently active user sessions |
+| Field           | Type    | Description |
+|-----------------|---------|-------------|
+| `name`          | string  | Server display name |
+| `version`       | string  | Server version |
+| `motd`          | string  | Message of the day |
+| `users`         | integer | Number of currently active user sessions |
+| `hashcash_bits` | integer | Required proof-of-work difficulty (leading zero bits). Only present when > 0. See [Hashcash Proof-of-Work](#hashcash-proof-of-work). |

 ### GET /.well-known/healthcheck.json — Health Check

@@ -1624,10 +1628,6 @@ authenticity.
  termination.
 - **CORS**: The server allows all origins by default (`Access-Control-Allow-Origin: *`).
  Restrict this in production via reverse proxy configuration if needed.
- **Content-Security-Policy**: The server sets a strict CSP header on all
-  responses, restricting resource loading to same-origin and disabling
-  dangerous features (object embeds, framing, base tag injection). The
-  embedded SPA works without `'unsafe-inline'` for scripts or styles.

 ---

@@ -1823,6 +1823,7 @@ directory is also loaded automatically via
 | `SENTRY_DSN`       | string  | `""`                                 | Sentry error tracking DSN (optional) |
 | `METRICS_USERNAME` | string  | `""`                                 | Basic auth username for `/metrics` endpoint. If empty, metrics endpoint is disabled. |
 | `METRICS_PASSWORD` | string  | `""`                                 | Basic auth password for `/metrics` endpoint |
+| `NEOIRC_HASHCASH_BITS` | int | `20`                               | Required hashcash proof-of-work difficulty (leading zero bits in SHA-256) for session creation. Set to `0` to disable. |
 | `MAINTENANCE_MODE` | bool    | `false`                              | Maintenance mode flag (reserved) |

 ### Example `.env` file
@@ -1834,6 +1835,7 @@ MOTD=Welcome! Be excellent to each other.
 DEBUG=false
 DBURL=file:///var/lib/neoirc/state.db?_journal_mode=WAL
 SESSION_IDLE_TIMEOUT=24h
+NEOIRC_HASHCASH_BITS=20
 ```

 ---
@@ -1856,16 +1858,16 @@ docker run -p 8080:8080 \
  neoirc
 ```

-The Dockerfile is a four-stage build:
-1. **web-builder**: Installs Node dependencies and compiles the SPA (JSX →
-   bundled JS via esbuild) into `web/dist/`
-2. **lint**: Runs formatting checks and golangci-lint against the Go source
-   (uses empty placeholder files for `web/dist/` so it runs independently of
-   web-builder for fast feedback)
-3. **builder**: Runs tests and compiles static `neoircd` and `neoirc-cli`
-   binaries with the real SPA assets from web-builder (CLI built to verify
-   compilation, not included in final image)
-4. **final**: Minimal Alpine image with only the `neoircd` binary
+The Dockerfile is a 4-stage build:
+1. **Web builder stage** (`web-builder`): Compiles the Preact JSX SPA into
+   static assets (`web/dist/`) using esbuild
+2. **Lint stage** (`lint`): Runs formatting checks and linting via golangci-lint
+3. **Build stage** (`builder`): Compiles `neoircd` and `neoirc-cli`, runs tests
+   (CLI built to verify compilation, not included in final image)
+4. **Runtime stage**: Alpine Linux + `neoircd` binary only
+
+`web/dist/` is not committed to git — it is built from `web/src/` by the
+web-builder stage during `docker build`.

 ### Binary

@@ -2106,62 +2108,102 @@ Clients should handle these message commands from the queue:

 ## Rate Limiting & Abuse Prevention

-Session creation (`POST /api/v1/session`) will require a
+### Hashcash Proof-of-Work
+
+Session creation (`POST /api/v1/session`) requires a
 [hashcash](https://en.wikipedia.org/wiki/Hashcash)-style proof-of-work token.
 This is the primary defense against resource exhaustion — no CAPTCHAs, no
 account registration, no IP-based rate limits that punish shared networks.

 ### How It Works

-1. Client requests a challenge: `GET /api/v1/challenge`
-   ```json
-   → {"nonce": "random-hex-string", "difficulty": 20, "expires": "2026-02-10T20:01:00Z"}
-   ```
-2. Server returns a nonce and a required difficulty (number of leading zero
-   bits in the SHA-256 hash)
-3. Client finds a counter value such that `SHA-256(nonce || ":" || counter)`
-   has the required number of leading zero bits:
-   ```
-   SHA-256("a1b2c3:0")     = 0xf3a1...  (0 leading zeros — no good)
-   SHA-256("a1b2c3:1")     = 0x8c72...  (0 leading zeros — no good)
-   ...
-   SHA-256("a1b2c3:94217") = 0x00003a... (20 leading zero bits — success!)
-   ```
-4. Client submits the proof with the session request:
-   ```json
-   POST /api/v1/session
-   {"nick": "alice", "proof": {"nonce": "a1b2c3", "counter": 94217}}
-   ```
-5. Server verifies:
-   - Nonce was issued by this server and hasn't expired
-   - Nonce hasn't been used before (prevent replay)
-   - `SHA-256(nonce || ":" || counter)` has the required leading zeros
-   - If valid, create the session normally
+1. Client fetches server info: `GET /api/v1/server` returns a `hashcash_bits`
+   field (e.g., `20`) indicating the required difficulty.
+2. Client computes a hashcash stamp: find a counter value such that the
+   SHA-256 hash of the stamp string has the required number of leading zero
+   bits.
+3. Client includes the stamp in the `X-Hashcash` request header when creating
+   a session: `POST /api/v1/session`.
+4. Server validates the stamp:
+   - Version is `1`
+   - Claimed bits ≥ required bits
+   - Resource matches the server name
+   - Date is within 48 hours (not expired, not too far in the future)
+   - SHA-256 hash has the required leading zero bits
+   - Stamp has not been used before (replay prevention)

-### Adaptive Difficulty
+### Stamp Format

-The required difficulty scales with server load. Under normal conditions, the
-cost is negligible (a few milliseconds of CPU). As concurrent sessions or
-session creation rate increases, difficulty rises — making bulk session creation
-exponentially more expensive for attackers while remaining cheap for legitimate
-single-user connections.
+Standard hashcash format:

-| Server Load        | Difficulty (bits) | Approx. Client CPU |
-|--------------------|-------------------|--------------------|
-| Normal (< 100/min) | 16                | ~1ms               |
-| Elevated           | 20                | ~15ms              |
-| High               | 24                | ~250ms             |
-| Under attack       | 28+               | ~4s+               |
+```
+1:bits:date:resource::counter
+```

-Each additional bit of difficulty doubles the expected work. An attacker
-creating 1000 sessions at difficulty 28 needs ~4000 CPU-seconds; a legitimate
-user creating one session needs ~4 seconds once and never again for the
-duration of their session.
+| Field      | Description |
+|------------|-------------|
+| `1`        | Version (always `1`) |
+| `bits`     | Claimed difficulty (must be ≥ server's `hashcash_bits`) |
+| `date`     | Date stamp in `YYMMDD` or `YYMMDDHHMMSS` format (UTC) |
+| `resource` | The server name (from `GET /api/v1/server`; defaults to `neoirc`) |
+| (empty)    | Extension field (unused) |
+| `counter`  | Hex counter value found by the client to satisfy the PoW |
+
+**Example stamp:** `1:20:260310:neoirc::3a2f1b`
+
+The SHA-256 hash of this entire string must have at least 20 leading zero bits.
+
+### Computing a Stamp
+
+```bash
+# Pseudocode
+bits = 20
+resource = "neoirc"
+date = "260310"         # YYMMDD in UTC
+counter = 0
+
+loop:
+    stamp = "1:{bits}:{date}:{resource}::{hex(counter)}"
+    hash = SHA-256(stamp)
+    if leading_zero_bits(hash) >= bits:
+        return stamp
+    counter++
+```
+
+At difficulty 20, this requires approximately 2^20 (~1M) hash attempts on
+average, taking roughly 0.5–2 seconds on modern hardware.
+
+### Client Integration
+
+Both the embedded web SPA and the CLI client automatically handle hashcash:
+
+1. Fetch `GET /api/v1/server` to read `hashcash_bits`
+2. If `hashcash_bits > 0`, compute a valid stamp
+3. Include the stamp in the `X-Hashcash` header on `POST /api/v1/session`
+
+The web SPA uses the Web Crypto API (`crypto.subtle.digest`) for SHA-256
+computation with batched parallelism. The CLI client uses Go's `crypto/sha256`.
+
+### Configuration
+
+Set `NEOIRC_HASHCASH_BITS` to control difficulty:
+
+| Value | Effect | Approx. Client CPU |
+|-------|--------|---------------------|
+| `0`   | Disabled (no proof-of-work required) | — |
+| `16`  | Light protection | ~1ms |
+| `20`  | Default — good balance | ~0.5–2s |
+| `24`  | Strong protection | ~10–30s |
+| `28`  | Very strong (may frustrate users) | ~2–10min |
+
+Each additional bit doubles the expected work. An attacker creating 1000
+sessions at difficulty 20 needs ~1000–2000 CPU-seconds; a legitimate user
+creating one session pays once and keeps their session.

 ### Why Hashcash and Not Rate Limits?

 - **No state to track**: No IP tables, no token buckets, no sliding windows.
-  The server only needs to verify a hash.
+  The server only needs to verify a single hash.
 - **Works through NATs and proxies**: Doesn't punish shared IPs (university
  campuses, corporate networks, Tor exits). Every client computes their own
  proof independently.
@@ -2169,36 +2211,9 @@ duration of their session.
  (one SHA-256 hash) regardless of difficulty. Only the client does more work.
 - **Fits the "no accounts" philosophy**: Proof-of-work is the cost of entry.
  No registration, no email, no phone number, no CAPTCHA. Just compute.
- **Trivial for legitimate clients**: A single-user client pays ~1ms of CPU
-  once. A botnet trying to create thousands of sessions pays exponentially more.
 - **Language-agnostic**: SHA-256 is available in every programming language.
  The proof computation is trivially implementable in any client.

-### Challenge Endpoint (Planned)
-
-```
-GET /api/v1/challenge
-```
-
-**Response:** `200 OK`
-```json
-{
-  "nonce": "a1b2c3d4e5f6...",
-  "difficulty": 20,
-  "algorithm": "sha256",
-  "expires": "2026-02-10T20:01:00Z"
-}
-```
-
-| Field        | Type    | Description |
-|--------------|---------|-------------|
-| `nonce`      | string  | Server-generated random hex string (32+ chars) |
-| `difficulty` | integer | Required number of leading zero bits in the hash |
-| `algorithm`  | string  | Hash algorithm (always `sha256` for now) |
-| `expires`    | string  | ISO 8601 expiry time for this challenge |
-
-**Status:** Not yet implemented. Tracked for post-MVP.
-
 ---

 ## Roadmap
@@ -2227,7 +2242,7 @@ GET /api/v1/challenge

 ### Post-MVP (Planned)

- [ ] **Hashcash proof-of-work** for session creation (abuse prevention)
+- [x] **Hashcash proof-of-work** for session creation (abuse prevention)
 - [ ] **Queue pruning** — delete old queue entries per `QUEUE_MAX_AGE`
 - [ ] **Message rotation** — enforce `MAX_HISTORY` per channel
 - [ ] **Channel modes** — enforce `+i`, `+m`, `+s`, `+t`, `+n`
@@ -2314,14 +2329,16 @@ neoirc/
 │       └── http.go         # HTTP timeouts
 ├── web/
 │   ├── embed.go            # go:embed directive for SPA
-│   ├── build.sh            # SPA build script (esbuild, runs in Docker)
-│   ├── package.json        # Node dependencies (preact, esbuild)
-│   ├── package-lock.json
-│   ├── src/                # SPA source files (JSX + HTML + CSS)
+│   ├── build.sh            # esbuild script: JSX → dist/
+│   ├── package.json        # Node dependencies (esbuild, preact)
+│   ├── src/                # SPA source (Preact JSX)
 │   │   ├── app.jsx
 │   │   ├── index.html
 │   │   └── style.css
-│   └── dist/               # Generated at Docker build time (not committed)
+│   └── dist/               # Built SPA (generated by web-builder Docker stage)
+│       ├── index.html
+│       ├── style.css
+│       └── app.js
 ├── schema/                 # JSON Schema definitions (planned)
 ├── go.mod
 ├── go.sum
@@ -2336,7 +2353,7 @@ neoirc/
 | Purpose    | Library |
 |------------|---------|
 | DI         | `go.uber.org/fx` |
-| Router     | `github.com/go-chi/chi/v5` |
+| Router     | `github.com/go-chi/chi` |
 | Logging    | `log/slog` (stdlib) |
 | Config     | `github.com/spf13/viper` |
 | Env        | `github.com/joho/godotenv/autoload` |
--- a/REPO_POLICIES.md
+++ b/REPO_POLICIES.md
@@ -1,6 +1,6 @@
 ---
 title: Repository Policies
-last_modified: 2026-03-09
+last_modified: 2026-02-22
 ---

 This document covers repository structure, tooling, and workflow standards. Code
@@ -98,13 +98,6 @@ style conventions are in separate documents:
  `https://git.eeqj.de/sneak/prompts/raw/branch/main/.gitignore` when setting up
  a new repo.

- **No build artifacts in version control.** Code-derived data (compiled
-  bundles, minified output, generated assets) must never be committed to the
-  repository if it can be avoided. The build process (e.g. Dockerfile, Makefile)
-  should generate these at build time. Notable exception: Go protobuf generated
-  files (`.pb.go`) ARE committed because repos need to work with `go get`, which
-  downloads code but does not execute code generation.
-
 - Never use `git add -A` or `git add .`. Always stage files explicitly by name.

 - Never force-push to `main`.
@@ -151,14 +144,8 @@ style conventions are in separate documents:
 - Use SemVer.

 - Database migrations live in `internal/db/migrations/` and must be embedded in
-  the binary.
-    - `000_migration.sql` — contains ONLY the creation of the migrations
-      tracking table itself. Nothing else.
-    - `001_schema.sql` — the full application schema.
-    - **Pre-1.0.0:** never add additional migration files (002, 003, etc.).
-      There is no installed base to migrate. Edit `001_schema.sql` directly.
-    - **Post-1.0.0:** add new numbered migration files for each schema change.
-      Never edit existing migrations after release.
+  the binary. Pre-1.0.0: modify existing migrations (no installed base assumed).
+  Post-1.0.0: add new migration files.

 - All repos should have an `.editorconfig` enforcing the project's indentation
  settings.
--- a/cmd/neoirc-cli/api/client.go
+++ b/cmd/neoirc-cli/api/client.go
@@ -43,13 +43,34 @@ func NewClient(baseURL string) *Client {
 }

 // CreateSession creates a new session on the server.
+// If the server requires hashcash proof-of-work, it
+// automatically fetches the difficulty and computes a
+// valid stamp.
 func (client *Client) CreateSession(
 	nick string,
 ) (*SessionResponse, error) {
-	data, err := client.do(
+	// Fetch server info to check for hashcash requirement.
+	info, err := client.GetServerInfo()
+
+	var headers map[string]string
+
+	if err == nil && info.HashcashBits > 0 {
+		resource := info.Name
+		if resource == "" {
+			resource = "neoirc"
+		}
+
+		stamp := MintHashcash(info.HashcashBits, resource)
+		headers = map[string]string{
+			"X-Hashcash": stamp,
+		}
+	}
+
+	data, err := client.doWithHeaders(
 		http.MethodPost,
 		"/api/v1/session",
 		&SessionRequest{Nick: nick},
+		headers,
 	)
 	if err != nil {
 		return nil, err
@@ -261,6 +282,16 @@ func (client *Client) GetServerInfo() (
 func (client *Client) do(
 	method, path string,
 	body any,
+) ([]byte, error) {
+	return client.doWithHeaders(
+		method, path, body, nil,
+	)
+}
+
+func (client *Client) doWithHeaders(
+	method, path string,
+	body any,
+	extraHeaders map[string]string,
 ) ([]byte, error) {
 	var bodyReader io.Reader

@@ -293,6 +324,10 @@ func (client *Client) do(
 		)
 	}

+	for key, val := range extraHeaders {
+		request.Header.Set(key, val)
+	}
+
 	resp, err := client.HTTPClient.Do(request)
 	if err != nil {
 		return nil, fmt.Errorf("http: %w", err)
--- a/cmd/neoirc-cli/api/hashcash.go
+++ b/cmd/neoirc-cli/api/hashcash.go
@@ -0,0 +1,79 @@
+package neoircapi
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"math/big"
+	"time"
+)
+
+const (
+	// bitsPerByte is the number of bits in a byte.
+	bitsPerByte = 8
+	// fullByteMask is 0xFF, a mask for all bits in a byte.
+	fullByteMask = 0xFF
+	// counterSpace is the range for random counter seeds.
+	counterSpace = 1 << 48
+)
+
+// MintHashcash computes a hashcash stamp with the given
+// difficulty (leading zero bits) and resource string.
+func MintHashcash(bits int, resource string) string {
+	date := time.Now().UTC().Format("060102")
+	prefix := fmt.Sprintf(
+		"1:%d:%s:%s::", bits, date, resource,
+	)
+
+	for {
+		counter := randomCounter()
+		stamp := prefix + counter
+		hash := sha256.Sum256([]byte(stamp))
+
+		if hasLeadingZeroBits(hash[:], bits) {
+			return stamp
+		}
+	}
+}
+
+// hasLeadingZeroBits checks if hash has at least numBits
+// leading zero bits.
+func hasLeadingZeroBits(
+	hash []byte,
+	numBits int,
+) bool {
+	fullBytes := numBits / bitsPerByte
+	remainBits := numBits % bitsPerByte
+
+	for idx := range fullBytes {
+		if hash[idx] != 0 {
+			return false
+		}
+	}
+
+	if remainBits > 0 && fullBytes < len(hash) {
+		mask := byte(
+			fullByteMask << (bitsPerByte - remainBits),
+		)
+
+		if hash[fullBytes]&mask != 0 {
+			return false
+		}
+	}
+
+	return true
+}
+
+// randomCounter generates a random hex counter string.
+func randomCounter() string {
+	counterVal, err := rand.Int(
+		rand.Reader, big.NewInt(counterSpace),
+	)
+	if err != nil {
+		// Fallback to timestamp-based counter on error.
+		return fmt.Sprintf("%x", time.Now().UnixNano())
+	}
+
+	return hex.EncodeToString(counterVal.Bytes())
+}
--- a/cmd/neoirc-cli/api/types.go
+++ b/cmd/neoirc-cli/api/types.go
@@ -63,9 +63,10 @@ type Channel struct {

 // ServerInfo is the response from GET /api/v1/server.
 type ServerInfo struct {
-	Name    string `json:"name"`
-	MOTD    string `json:"motd"`
-	Version string `json:"version"`
+	Name         string `json:"name"`
+	MOTD         string `json:"motd"`
+	Version      string `json:"version"`
+	HashcashBits int    `json:"hashcash_bits"` //nolint:tagliatelle
 }

 // MessagesResponse wraps polling results.
--- a/go.mod
+++ b/go.mod
@@ -6,7 +6,7 @@ require (
 	github.com/99designs/basicauth-go v0.0.0-20230316000542-bf6f9cbbf0f8
 	github.com/gdamore/tcell/v2 v2.13.8
 	github.com/getsentry/sentry-go v0.42.0
-	github.com/go-chi/chi/v5 v5.2.1
+	github.com/go-chi/chi v1.5.5
 	github.com/go-chi/cors v1.2.2
 	github.com/google/uuid v1.6.0
 	github.com/joho/godotenv v1.5.1
--- a/go.sum
+++ b/go.sum
@@ -18,8 +18,8 @@ github.com/gdamore/tcell/v2 v2.13.8 h1:Mys/Kl5wfC/GcC5Cx4C2BIQH9dbnhnkPgS9/wF3Rl
 github.com/gdamore/tcell/v2 v2.13.8/go.mod h1:+Wfe208WDdB7INEtCsNrAN6O2m+wsTPk1RAovjaILlo=
 github.com/getsentry/sentry-go v0.42.0 h1:eeFMACuZTbUQf90RE8dE4tXeSe4CZyfvR1MBL7RLEt8=
 github.com/getsentry/sentry-go v0.42.0/go.mod h1:eRXCoh3uvmjQLY6qu63BjUZnaBu5L5WhMV1RwYO8W5s=
-github.com/go-chi/chi/v5 v5.2.1 h1:KOIHODQj58PmL80G2Eak4WdvUzjSJSm0vG72crDCqb8=
-github.com/go-chi/chi/v5 v5.2.1/go.mod h1:L2yAIGWB3H+phAw1NxKwWM+7eUH/lU8pOMm5hHcoops=
+github.com/go-chi/chi v1.5.5 h1:vOB/HbEMt9QqBqErz07QehcOKHaWFtuj87tTDVz2qXE=
+github.com/go-chi/chi v1.5.5/go.mod h1:C9JqLr3tIYjDOZpzn+BCuxY8z8vmca43EeMgyZt7irw=
 github.com/go-chi/cors v1.2.2 h1:Jmey33TE+b+rB7fT8MUy1u0I4L+NARQlK6LhzKPSyQE=
 github.com/go-chi/cors v1.2.2/go.mod h1:sSbTewc+6wYHBBCW7ytsFSn836hqM7JxpglAy2Vzc58=
 github.com/go-errors/errors v1.4.2 h1:J6MZopCL4uSllY1OfXM374weqZFFItUbrImctkmUxIA=
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -44,6 +44,7 @@ type Config struct {
 	ServerName         string
 	FederationKey      string
 	SessionIdleTimeout string
+	HashcashBits       int
 	params             *Params
 	log                *slog.Logger
 }
@@ -74,6 +75,7 @@ func New(
 	viper.SetDefault("SERVER_NAME", "")
 	viper.SetDefault("FEDERATION_KEY", "")
 	viper.SetDefault("SESSION_IDLE_TIMEOUT", "24h")
+	viper.SetDefault("NEOIRC_HASHCASH_BITS", "20")

 	err := viper.ReadInConfig()
 	if err != nil {
@@ -98,6 +100,7 @@ func New(
 		ServerName:         viper.GetString("SERVER_NAME"),
 		FederationKey:      viper.GetString("FEDERATION_KEY"),
 		SessionIdleTimeout: viper.GetString("SESSION_IDLE_TIMEOUT"),
+		HashcashBits:       viper.GetInt("NEOIRC_HASHCASH_BITS"),
 		log:                log,
 		params:             &params,
 	}
--- a/internal/db/auth.go
+++ b/internal/db/auth.go
@@ -64,14 +64,12 @@ func (database *Database) RegisterUser(

 	sessionID, _ := res.LastInsertId()

-	tokenHash := hashToken(token)
-
 	clientRes, err := transaction.ExecContext(ctx,
 		`INSERT INTO clients
 		 (uuid, session_id, token,
 		  created_at, last_seen)
 		 VALUES (?, ?, ?, ?, ?)`,
-		clientUUID, sessionID, tokenHash, now, now)
+		clientUUID, sessionID, token, now, now)
 	if err != nil {
 		_ = transaction.Rollback()

@@ -139,14 +137,12 @@ func (database *Database) LoginUser(

 	now := time.Now()

-	tokenHash := hashToken(token)
-
 	res, err := database.conn.ExecContext(ctx,
 		`INSERT INTO clients
 		 (uuid, session_id, token,
 		  created_at, last_seen)
 		 VALUES (?, ?, ?, ?, ?)`,
-		clientUUID, sessionID, tokenHash, now, now)
+		clientUUID, sessionID, token, now, now)
 	if err != nil {
 		return 0, 0, "", fmt.Errorf(
 			"create login client: %w", err,
--- a/internal/db/errors.go
+++ b/internal/db/errors.go
@@ -1,20 +0,0 @@
-// Package db provides database access and migration management.
-package db
-
-import (
-	"errors"
-
-	"modernc.org/sqlite"
-	sqlite3 "modernc.org/sqlite/lib"
-)
-
-// IsUniqueConstraintError reports whether err is a SQLite
-// unique-constraint violation.
-func IsUniqueConstraintError(err error) bool {
-	var sqliteErr *sqlite.Error
-	if !errors.As(err, &sqliteErr) {
-		return false
-	}
-
-	return sqliteErr.Code() == sqlite3.SQLITE_CONSTRAINT_UNIQUE
-}
--- a/internal/db/queries.go
+++ b/internal/db/queries.go
@@ -3,7 +3,6 @@ package db
 import (
 	"context"
 	"crypto/rand"
-	"crypto/sha256"
 	"database/sql"
 	"encoding/hex"
 	"encoding/json"
@@ -32,14 +31,6 @@ func generateToken() (string, error) {
 	return hex.EncodeToString(buf), nil
 }

-// hashToken returns the lowercase hex-encoded SHA-256
-// digest of a plaintext token string.
-func hashToken(token string) string {
-	sum := sha256.Sum256([]byte(token))
-
-	return hex.EncodeToString(sum[:])
-}
-
 // IRCMessage is the IRC envelope for all messages.
 type IRCMessage struct {
 	ID      string          `json:"id"`
@@ -114,14 +105,12 @@ func (database *Database) CreateSession(

 	sessionID, _ := res.LastInsertId()

-	tokenHash := hashToken(token)
-
 	clientRes, err := transaction.ExecContext(ctx,
 		`INSERT INTO clients
 		 (uuid, session_id, token,
 		  created_at, last_seen)
 		 VALUES (?, ?, ?, ?, ?)`,
-		clientUUID, sessionID, tokenHash, now, now)
+		clientUUID, sessionID, token, now, now)
 	if err != nil {
 		_ = transaction.Rollback()

@@ -154,8 +143,6 @@ func (database *Database) GetSessionByToken(
 		nick      string
 	)

-	tokenHash := hashToken(token)
-
 	err := database.conn.QueryRowContext(
 		ctx,
 		`SELECT s.id, c.id, s.nick
@@ -163,7 +150,7 @@ func (database *Database) GetSessionByToken(
 		 INNER JOIN sessions s
 		   ON s.id = c.session_id
 		 WHERE c.token = ?`,
-		tokenHash,
+		token,
 	).Scan(&sessionID, &clientID, &nick)
 	if err != nil {
 		return 0, 0, "", fmt.Errorf(
--- a/internal/handlers/api.go
+++ b/internal/handlers/api.go
@@ -10,9 +10,8 @@ import (
 	"strings"
 	"time"

-	"git.eeqj.de/sneak/neoirc/internal/db"
 	"git.eeqj.de/sneak/neoirc/internal/irc"
-	"github.com/go-chi/chi/v5"
+	"github.com/go-chi/chi"
 )

 var validNickRe = regexp.MustCompile(
@@ -145,6 +144,33 @@ func (hdlr *Handlers) handleCreateSession(
 	writer http.ResponseWriter,
 	request *http.Request,
 ) {
+	// Validate hashcash proof-of-work if configured.
+	if hdlr.params.Config.HashcashBits > 0 {
+		stamp := request.Header.Get("X-Hashcash")
+		if stamp == "" {
+			hdlr.respondError(
+				writer, request,
+				"hashcash proof-of-work required",
+				http.StatusPaymentRequired,
+			)
+
+			return
+		}
+
+		err := hdlr.hashcashVal.Validate(
+			stamp, hdlr.params.Config.HashcashBits,
+		)
+		if err != nil {
+			hdlr.respondError(
+				writer, request,
+				"invalid hashcash stamp: "+err.Error(),
+				http.StatusPaymentRequired,
+			)
+
+			return
+		}
+	}
+
 	type createRequest struct {
 		Nick string `json:"nick"`
 	}
@@ -200,7 +226,7 @@ func (hdlr *Handlers) handleCreateSessionError(
 	request *http.Request,
 	err error,
 ) {
-	if db.IsUniqueConstraintError(err) {
+	if strings.Contains(err.Error(), "UNIQUE") {
 		hdlr.respondError(
 			writer, request,
 			"nick already taken",
@@ -445,17 +471,13 @@ func (hdlr *Handlers) enqueueNumeric(
 }

 // HandleState returns the current session's info and
-// channels.  When called with ?initChannelState=1, it also
-// enqueues synthetic JOIN + TOPIC + NAMES messages for
-// every channel the session belongs to so that a
-// reconnecting client can rebuild its channel tabs from
-// the message stream.
+// channels.
 func (hdlr *Handlers) HandleState() http.HandlerFunc {
 	return func(
 		writer http.ResponseWriter,
 		request *http.Request,
 	) {
-		sessionID, clientID, nick, ok :=
+		sessionID, _, nick, ok :=
 			hdlr.requireAuth(writer, request)
 		if !ok {
 			return
@@ -477,12 +499,6 @@ func (hdlr *Handlers) HandleState() http.HandlerFunc {
 			return
 		}

-		if request.URL.Query().Get("initChannelState") == "1" {
-			hdlr.initChannelState(
-				request, clientID, sessionID, nick,
-			)
-		}
-
 		hdlr.respondJSON(writer, request, map[string]any{
 			"id":       sessionID,
 			"nick":     nick,
@@ -491,52 +507,6 @@ func (hdlr *Handlers) HandleState() http.HandlerFunc {
 	}
 }

-// initChannelState enqueues synthetic JOIN messages and
-// join-numerics (TOPIC, NAMES) for every channel the
-// session belongs to.  Messages are enqueued only to the
-// specified client so other clients/sessions are not
-// affected.
-func (hdlr *Handlers) initChannelState(
-	request *http.Request,
-	clientID, sessionID int64,
-	nick string,
-) {
-	ctx := request.Context()
-
-	channels, err := hdlr.params.Database.
-		GetSessionChannels(ctx, sessionID)
-	if err != nil || len(channels) == 0 {
-		return
-	}
-
-	for _, chanInfo := range channels {
-		// Enqueue a synthetic JOIN (only to this client).
-		dbID, _, insErr := hdlr.params.Database.
-			InsertMessage(
-				ctx, "JOIN", nick, chanInfo.Name,
-				nil, nil, nil,
-			)
-		if insErr != nil {
-			hdlr.log.Error(
-				"initChannelState: insert JOIN",
-				"error", insErr,
-			)
-
-			continue
-		}
-
-		_ = hdlr.params.Database.EnqueueToClient(
-			ctx, clientID, dbID,
-		)
-
-		// Enqueue TOPIC + NAMES numerics.
-		hdlr.deliverJoinNumerics(
-			request, clientID, sessionID,
-			nick, chanInfo.Name, chanInfo.ID,
-		)
-	}
-}
-
 // HandleListAllChannels returns all channels on the server.
 func (hdlr *Handlers) HandleListAllChannels() http.HandlerFunc {
 	return func(
@@ -1428,7 +1398,7 @@ func (hdlr *Handlers) executeNickChange(
 		request.Context(), sessionID, newNick,
 	)
 	if err != nil {
-		if db.IsUniqueConstraintError(err) {
+		if strings.Contains(err.Error(), "UNIQUE") {
 			hdlr.respondIRCError(
 				writer, request, clientID, sessionID,
 				irc.ErrNicknameInUse, nick, []string{newNick},
@@ -2392,11 +2362,19 @@ func (hdlr *Handlers) HandleServerInfo() http.HandlerFunc {
 			return
 		}

-		hdlr.respondJSON(writer, request, map[string]any{
+		resp := map[string]any{
 			"name":    hdlr.params.Config.ServerName,
 			"version": hdlr.params.Globals.Version,
 			"motd":    hdlr.params.Config.MOTD,
 			"users":   users,
-		}, http.StatusOK)
+		}
+
+		if hdlr.params.Config.HashcashBits > 0 {
+			resp["hashcash_bits"] = hdlr.params.Config.HashcashBits
+		}
+
+		hdlr.respondJSON(
+			writer, request, resp, http.StatusOK,
+		)
 	}
 }
--- a/internal/handlers/api_test.go
+++ b/internal/handlers/api_test.go
@@ -85,6 +85,7 @@ func newTestServer(

 				cfg.DBURL = dbURL
 				cfg.Port = 0
+				cfg.HashcashBits = 0

 				return cfg, nil
 			},
--- a/internal/handlers/auth.go
+++ b/internal/handlers/auth.go
@@ -4,8 +4,6 @@ import (
 	"encoding/json"
 	"net/http"
 	"strings"
-
-	"git.eeqj.de/sneak/neoirc/internal/db"
 )

 const minPasswordLength = 8
@@ -96,7 +94,7 @@ func (hdlr *Handlers) handleRegisterError(
 	request *http.Request,
 	err error,
 ) {
-	if db.IsUniqueConstraintError(err) {
+	if strings.Contains(err.Error(), "UNIQUE") {
 		hdlr.respondError(
 			writer, request,
 			"nick already taken",
@@ -184,12 +182,6 @@ func (hdlr *Handlers) handleLogin(
 		request, clientID, sessionID, payload.Nick,
 	)

-	// Initialize channel state so the new client knows
-	// which channels the session already belongs to.
-	hdlr.initChannelState(
-		request, clientID, sessionID, payload.Nick,
-	)
-
 	hdlr.respondJSON(writer, request, map[string]any{
 		"id":    sessionID,
 		"nick":  payload.Nick,
--- a/internal/handlers/handlers.go
+++ b/internal/handlers/handlers.go
@@ -13,6 +13,7 @@ import (
 	"git.eeqj.de/sneak/neoirc/internal/config"
 	"git.eeqj.de/sneak/neoirc/internal/db"
 	"git.eeqj.de/sneak/neoirc/internal/globals"
+	"git.eeqj.de/sneak/neoirc/internal/hashcash"
 	"git.eeqj.de/sneak/neoirc/internal/healthcheck"
 	"git.eeqj.de/sneak/neoirc/internal/logger"
 	"go.uber.org/fx"
@@ -39,6 +40,7 @@ type Handlers struct {
 	log           *slog.Logger
 	hc            *healthcheck.Healthcheck
 	broker        *broker.Broker
+	hashcashVal   *hashcash.Validator
 	cancelCleanup context.CancelFunc
 }

@@ -47,11 +49,17 @@ func New(
 	lifecycle fx.Lifecycle,
 	params Params,
 ) (*Handlers, error) {
+	resource := params.Config.ServerName
+	if resource == "" {
+		resource = "neoirc"
+	}
+
 	hdlr := &Handlers{ //nolint:exhaustruct // cancelCleanup set in startCleanup
-		params: &params,
-		log:    params.Logger.Get(),
-		hc:     params.Healthcheck,
-		broker: broker.New(),
+		params:      &params,
+		log:         params.Logger.Get(),
+		hc:          params.Healthcheck,
+		broker:      broker.New(),
+		hashcashVal: hashcash.NewValidator(resource),
 	}

 	lifecycle.Append(fx.Hook{
--- a/internal/hashcash/hashcash.go
+++ b/internal/hashcash/hashcash.go
@@ -0,0 +1,277 @@
+// Package hashcash implements SHA-256-based hashcash
+// proof-of-work validation for abuse prevention.
+//
+// Stamp format: 1:bits:YYMMDD:resource::counter.
+//
+// The SHA-256 hash of the entire stamp string must have
+// at least `bits` leading zero bits.
+package hashcash
+
+import (
+	"crypto/sha256"
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+)
+
+const (
+	// stampVersion is the only supported hashcash version.
+	stampVersion = "1"
+	// stampFields is the number of fields in a stamp.
+	stampFields = 6
+	// maxStampAge is how old a stamp can be before
+	// rejection.
+	maxStampAge = 48 * time.Hour
+	// maxFutureSkew allows stamps slightly in the future.
+	maxFutureSkew = 1 * time.Hour
+	// pruneInterval controls how often expired stamps are
+	// removed from the spent set.
+	pruneInterval = 10 * time.Minute
+	// dateFormatShort is the YYMMDD date layout.
+	dateFormatShort = "060102"
+	// dateFormatLong is the YYMMDDHHMMSS date layout.
+	dateFormatLong = "060102150405"
+	// dateShortLen is the length of YYMMDD.
+	dateShortLen = 6
+	// dateLongLen is the length of YYMMDDHHMMSS.
+	dateLongLen = 12
+	// bitsPerByte is the number of bits in a byte.
+	bitsPerByte = 8
+	// fullByteMask is 0xFF, a mask for all bits in a byte.
+	fullByteMask = 0xFF
+)
+
+var (
+	errInvalidFields    = errors.New("invalid stamp field count")
+	errBadVersion       = errors.New("unsupported stamp version")
+	errInsufficientBits = errors.New("insufficient difficulty")
+	errWrongResource    = errors.New("wrong resource")
+	errStampExpired     = errors.New("stamp expired")
+	errStampFuture      = errors.New("stamp date in future")
+	errProofFailed      = errors.New("proof-of-work failed")
+	errStampReused      = errors.New("stamp already used")
+	errBadDateFormat    = errors.New("unrecognized date format")
+)
+
+// Validator checks hashcash stamps for validity and
+// prevents replay attacks via an in-memory spent set.
+type Validator struct {
+	resource string
+	mu       sync.Mutex
+	spent    map[string]time.Time
+}
+
+// NewValidator creates a Validator for the given resource.
+func NewValidator(resource string) *Validator {
+	validator := &Validator{
+		resource: resource,
+		mu:       sync.Mutex{},
+		spent:    make(map[string]time.Time),
+	}
+
+	go validator.pruneLoop()
+
+	return validator
+}
+
+// Validate checks a hashcash stamp. It returns nil if the
+// stamp is valid and has not been seen before.
+func (v *Validator) Validate(
+	stamp string,
+	requiredBits int,
+) error {
+	if requiredBits <= 0 {
+		return nil
+	}
+
+	parts := strings.Split(stamp, ":")
+	if len(parts) != stampFields {
+		return fmt.Errorf(
+			"%w: expected %d, got %d",
+			errInvalidFields, stampFields, len(parts),
+		)
+	}
+
+	version := parts[0]
+	bitsStr := parts[1]
+	dateStr := parts[2]
+	resource := parts[3]
+
+	if err := v.validateHeader(
+		version, bitsStr, resource, requiredBits,
+	); err != nil {
+		return err
+	}
+
+	stampTime, err := parseStampDate(dateStr)
+	if err != nil {
+		return err
+	}
+
+	if err := validateTime(stampTime); err != nil {
+		return err
+	}
+
+	if err := validateProof(
+		stamp, requiredBits,
+	); err != nil {
+		return err
+	}
+
+	return v.checkAndRecordStamp(stamp, stampTime)
+}
+
+func (v *Validator) validateHeader(
+	version, bitsStr, resource string,
+	requiredBits int,
+) error {
+	if version != stampVersion {
+		return fmt.Errorf(
+			"%w: %s", errBadVersion, version,
+		)
+	}
+
+	claimedBits, err := strconv.Atoi(bitsStr)
+	if err != nil || claimedBits < requiredBits {
+		return fmt.Errorf(
+			"%w: need %d bits",
+			errInsufficientBits, requiredBits,
+		)
+	}
+
+	if resource != v.resource {
+		return fmt.Errorf(
+			"%w: got %q, want %q",
+			errWrongResource, resource, v.resource,
+		)
+	}
+
+	return nil
+}
+
+func validateTime(stampTime time.Time) error {
+	now := time.Now()
+
+	if now.Sub(stampTime) > maxStampAge {
+		return errStampExpired
+	}
+
+	if stampTime.Sub(now) > maxFutureSkew {
+		return errStampFuture
+	}
+
+	return nil
+}
+
+func validateProof(stamp string, requiredBits int) error {
+	hash := sha256.Sum256([]byte(stamp))
+	if !hasLeadingZeroBits(hash[:], requiredBits) {
+		return fmt.Errorf(
+			"%w: need %d leading zero bits",
+			errProofFailed, requiredBits,
+		)
+	}
+
+	return nil
+}
+
+func (v *Validator) checkAndRecordStamp(
+	stamp string,
+	stampTime time.Time,
+) error {
+	v.mu.Lock()
+	defer v.mu.Unlock()
+
+	if _, ok := v.spent[stamp]; ok {
+		return errStampReused
+	}
+
+	v.spent[stamp] = stampTime
+
+	return nil
+}
+
+// hasLeadingZeroBits checks if the hash has at least n
+// leading zero bits.
+func hasLeadingZeroBits(hash []byte, numBits int) bool {
+	fullBytes := numBits / bitsPerByte
+	remainBits := numBits % bitsPerByte
+
+	for idx := range fullBytes {
+		if hash[idx] != 0 {
+			return false
+		}
+	}
+
+	if remainBits > 0 && fullBytes < len(hash) {
+		mask := byte(
+			fullByteMask << (bitsPerByte - remainBits),
+		)
+
+		if hash[fullBytes]&mask != 0 {
+			return false
+		}
+	}
+
+	return true
+}
+
+// parseStampDate parses a hashcash date stamp.
+// Supports YYMMDD and YYMMDDHHMMSS formats.
+func parseStampDate(dateStr string) (time.Time, error) {
+	switch len(dateStr) {
+	case dateShortLen:
+		parsed, err := time.Parse(
+			dateFormatShort, dateStr,
+		)
+		if err != nil {
+			return time.Time{}, fmt.Errorf(
+				"parse date: %w", err,
+			)
+		}
+
+		return parsed, nil
+	case dateLongLen:
+		parsed, err := time.Parse(
+			dateFormatLong, dateStr,
+		)
+		if err != nil {
+			return time.Time{}, fmt.Errorf(
+				"parse date: %w", err,
+			)
+		}
+
+		return parsed, nil
+	default:
+		return time.Time{}, fmt.Errorf(
+			"%w: %q", errBadDateFormat, dateStr,
+		)
+	}
+}
+
+// pruneLoop periodically removes expired stamps from the
+// spent set.
+func (v *Validator) pruneLoop() {
+	ticker := time.NewTicker(pruneInterval)
+	defer ticker.Stop()
+
+	for range ticker.C {
+		v.prune()
+	}
+}
+
+func (v *Validator) prune() {
+	cutoff := time.Now().Add(-maxStampAge)
+
+	v.mu.Lock()
+	defer v.mu.Unlock()
+
+	for stamp, stampTime := range v.spent {
+		if stampTime.Before(cutoff) {
+			delete(v.spent, stamp)
+		}
+	}
+}
--- a/internal/middleware/middleware.go
+++ b/internal/middleware/middleware.go
@@ -11,7 +11,7 @@ import (
 	"git.eeqj.de/sneak/neoirc/internal/globals"
 	"git.eeqj.de/sneak/neoirc/internal/logger"
 	basicauth "github.com/99designs/basicauth-go"
-	chimw "github.com/go-chi/chi/v5/middleware"
+	chimw "github.com/go-chi/chi/middleware"
 	"github.com/go-chi/cors"
 	metrics "github.com/slok/go-http-metrics/metrics/prometheus"
 	ghmm "github.com/slok/go-http-metrics/middleware"
@@ -142,6 +142,20 @@ func (mware *Middleware) CORS() func(http.Handler) http.Handler {
 	})
 }

+// Auth returns middleware that performs authentication.
+func (mware *Middleware) Auth() func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(
+			func(
+				writer http.ResponseWriter,
+				request *http.Request,
+			) {
+				mware.log.Info("AUTH: before request")
+				next.ServeHTTP(writer, request)
+			})
+	}
+}
+
 // Metrics returns middleware that records HTTP metrics.
 func (mware *Middleware) Metrics() func(http.Handler) http.Handler {
 	metricsMiddleware := ghmm.New(ghmm.Config{ //nolint:exhaustruct // optional fields
@@ -166,36 +180,3 @@ func (mware *Middleware) MetricsAuth() func(http.Handler) http.Handler {
 		},
 	)
 }
-
-// cspPolicy is the Content-Security-Policy header value applied to all
-// responses.  The embedded SPA loads scripts and styles from same-origin
-// files only (no inline scripts or inline style attributes), so a strict
-// policy works without 'unsafe-inline'.
-const cspPolicy = "default-src 'self'; " +
-	"script-src 'self'; " +
-	"style-src 'self'; " +
-	"connect-src 'self'; " +
-	"img-src 'self'; " +
-	"font-src 'self'; " +
-	"object-src 'none'; " +
-	"frame-ancestors 'none'; " +
-	"base-uri 'self'; " +
-	"form-action 'self'"
-
-// CSP returns middleware that sets the Content-Security-Policy header on
-// every response for defense-in-depth against XSS.
-func (mware *Middleware) CSP() func(http.Handler) http.Handler {
-	return func(next http.Handler) http.Handler {
-		return http.HandlerFunc(
-			func(
-				writer http.ResponseWriter,
-				request *http.Request,
-			) {
-				writer.Header().Set(
-					"Content-Security-Policy",
-					cspPolicy,
-				)
-				next.ServeHTTP(writer, request)
-			})
-	}
-}
--- a/internal/server/routes.go
+++ b/internal/server/routes.go
@@ -8,8 +8,8 @@ import (
 	"git.eeqj.de/sneak/neoirc/web"

 	sentryhttp "github.com/getsentry/sentry-go/http"
-	"github.com/go-chi/chi/v5"
-	"github.com/go-chi/chi/v5/middleware"
+	"github.com/go-chi/chi"
+	"github.com/go-chi/chi/middleware"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/spf13/viper"
 )
@@ -29,7 +29,6 @@ func (srv *Server) SetupRoutes() {
 	}

 	srv.router.Use(srv.mw.CORS())
-	srv.router.Use(srv.mw.CSP())
 	srv.router.Use(middleware.Timeout(routeTimeout))

 	if srv.sentryEnabled {
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -20,7 +20,7 @@ import (
 	"go.uber.org/fx"

 	"github.com/getsentry/sentry-go"
-	"github.com/go-chi/chi/v5"
+	"github.com/go-chi/chi"

 	_ "github.com/joho/godotenv/autoload" // loads .env file
 )
--- a/web/src/app.jsx
+++ b/web/src/app.jsx
@@ -8,6 +8,56 @@ const MEMBER_REFRESH_INTERVAL = 10000;
 const ACTION_PREFIX = "\x01ACTION ";
 const ACTION_SUFFIX = "\x01";

+// Hashcash proof-of-work helpers using Web Crypto API.
+
+function checkLeadingZeros(hashBytes, bits) {
+  let count = 0;
+  for (let i = 0; i < hashBytes.length; i++) {
+    if (hashBytes[i] === 0) {
+      count += 8;
+      continue;
+    }
+    let b = hashBytes[i];
+    while ((b & 0x80) === 0) {
+      count++;
+      b <<= 1;
+    }
+    break;
+  }
+  return count >= bits;
+}
+
+async function mintHashcash(bits, resource) {
+  const encoder = new TextEncoder();
+  const now = new Date();
+  const date =
+    String(now.getUTCFullYear()).slice(2) +
+    String(now.getUTCMonth() + 1).padStart(2, "0") +
+    String(now.getUTCDate()).padStart(2, "0");
+  const prefix = `1:${bits}:${date}:${resource}::`;
+  let nonce = Math.floor(Math.random() * 0x100000);
+  const batchSize = 1024;
+
+  for (;;) {
+    const stamps = [];
+    const hashPromises = [];
+    for (let i = 0; i < batchSize; i++) {
+      const stamp = prefix + (nonce + i).toString(16);
+      stamps.push(stamp);
+      hashPromises.push(
+        crypto.subtle.digest("SHA-256", encoder.encode(stamp)),
+      );
+    }
+    const hashes = await Promise.all(hashPromises);
+    for (let i = 0; i < hashes.length; i++) {
+      if (checkLeadingZeros(new Uint8Array(hashes[i]), bits)) {
+        return stamps[i];
+      }
+    }
+    nonce += batchSize;
+  }
+}
+
 function api(path, opts = {}) {
  const token = localStorage.getItem("neoirc_token");
  const headers = {
@@ -60,17 +110,21 @@ function LoginScreen({ onLogin }) {
  const [motd, setMotd] = useState("");
  const [serverName, setServerName] = useState("NeoIRC");
  const inputRef = useRef();
+  const hashcashBitsRef = useRef(0);
+  const hashcashResourceRef = useRef("neoirc");

  useEffect(() => {
    api("/server")
      .then((s) => {
        if (s.name) setServerName(s.name);
        if (s.motd) setMotd(s.motd);
+        hashcashBitsRef.current = s.hashcash_bits || 0;
+        if (s.name) hashcashResourceRef.current = s.name;
      })
      .catch(() => {});
    const saved = localStorage.getItem("neoirc_token");
    if (saved) {
-      api("/state?initChannelState=1")
+      api("/state")
        .then((u) => onLogin(u.nick, true))
        .catch(() => localStorage.removeItem("neoirc_token"));
    }
@@ -81,9 +135,20 @@ function LoginScreen({ onLogin }) {
    e.preventDefault();
    setError("");
    try {
+      const extraHeaders = {};
+      if (hashcashBitsRef.current > 0) {
+        setError("Computing proof-of-work...");
+        const stamp = await mintHashcash(
+          hashcashBitsRef.current,
+          hashcashResourceRef.current,
+        );
+        extraHeaders["X-Hashcash"] = stamp;
+        setError("");
+      }
      const res = await api("/session", {
        method: "POST",
        body: JSON.stringify({ nick: nick.trim() }),
+        headers: extraHeaders,
      });
      localStorage.setItem("neoirc_token", res.token);
      onLogin(res.nick);
@@ -333,24 +398,7 @@ function App() {
        case "JOIN": {
          const text = `${msg.from} has joined ${msg.to}`;
          if (msg.to) addMessage(msg.to, { ...base, text, system: true });
-          if (msg.to && msg.to.startsWith("#")) {
-            // Create a tab when the current user joins a channel
-            // (including JOINs from initChannelState on reconnect).
-            if (msg.from === nickRef.current) {
-              setTabs((prev) => {
-                if (
-                  prev.find(
-                    (t) => t.type === "channel" && t.name === msg.to,
-                  )
-                )
-                  return prev;
-
-                return [...prev, { type: "channel", name: msg.to }];
-              });
-            }
-
-            refreshMembers(msg.to);
-          }
+          if (msg.to && msg.to.startsWith("#")) refreshMembers(msg.to);

          break;
        }
@@ -653,13 +701,9 @@ function App() {
      setLoggedIn(true);
      addSystemMessage("Server", `Connected as ${userNick}`);

+      // Request MOTD on resumed sessions (new sessions get
+      // it automatically from the server during creation).
      if (isResumed) {
-        // Request MOTD on resumed sessions (new sessions
-        // get it automatically from the server during
-        // creation).  Channel state is initialized by the
-        // server via the message queue
-        // (?initChannelState=1), so we do not need to
-        // re-JOIN channels here.
        try {
          await api("/messages", {
            method: "POST",
@@ -668,11 +712,8 @@ function App() {
        } catch (e) {
          // MOTD is non-critical.
        }
-
-        return;
      }

-      // Fresh session — join any previously saved channels.
      const saved = JSON.parse(
        localStorage.getItem("neoirc_channels") || "[]",
      );