- Move H from Type B to Type C in CHANMODES ISUPPORT string (H takes
a parameter only when set, not when unset)
- Refactor MintChannelHashcash to delegate to hashcash.BodyHash() and
hashcash.MintChannelStamp() instead of reimplementing them
Add per-channel hashcash requirement via MODE +H <bits>. When set,
PRIVMSG to the channel must include a valid hashcash stamp in the
meta.hashcash field bound to the channel name and message body hash.
Server validates stamp format, difficulty, date freshness, channel
binding, body hash binding, and proof-of-work. Spent stamps are
persisted to SQLite with 1-year TTL for replay prevention.
Stamp format: 1:bits:YYMMDD:channel:bodyhash:counter
Changes:
- Schema: add hashcash_bits column to channels, spent_hashcash table
- DB: queries for get/set channel hashcash bits, spent token CRUD
- Hashcash: ChannelValidator, BodyHash, StampHash, MintChannelStamp
- Handlers: validate hashcash on PRIVMSG, MODE +H/-H support
- Pass meta through fanOut chain to store in messages
- Prune spent hashcash tokens in cleanup loop (1-year TTL)
- Client: MintChannelHashcash helper for CLI
- Tests: 12 new channel_test.go + 10 new api_test.go integration tests
- README: document +H mode, stamp format, and usage
## Summary
Implement SHA-256-based hashcash proof-of-work for `POST /session` to prevent abuse via rapid session creation.
closes #11
## What Changed
### Server
- **New `internal/hashcash` package**: Validates hashcash stamps (format, difficulty bits, date/expiry, resource, replay prevention via in-memory spent set with TTL pruning)
- **Config**: `NEOIRC_HASHCASH_BITS` env var (default 20, set to 0 to disable)
- **`GET /api/v1/server`**: Now includes `hashcash_bits` field when > 0
- **`POST /api/v1/session`**: Validates `X-Hashcash` header when hashcash is enabled; returns HTTP 402 for missing/invalid stamps
### Clients
- **Web SPA**: Fetches `hashcash_bits` from `/server`, computes stamp using Web Crypto API (`crypto.subtle.digest`) with batched parallelism (1024 hashes/batch), shows "Computing proof-of-work..." feedback
- **CLI (`neoirc-cli`)**: `CreateSession()` auto-fetches server info and computes a valid hashcash stamp when required; new `MintHashcash()` function in the API package
### Documentation
- README updated with full hashcash documentation: stamp format, computing stamps, configuration, difficulty table
- Server info and session creation API docs updated with hashcash fields/headers
- Roadmap updated (hashcash marked as implemented)
## Stamp Format
Standard hashcash: `1:bits:YYMMDD:resource::counter`
The SHA-256 hash of the entire stamp string must have at least `bits` leading zero bits.
## Validation Rules
- Version must be `1`
- Claimed bits ≥ required bits
- Resource must match server name
- Date within 48 hours (not expired, not too far in future)
- SHA-256 hash has required leading zero bits
- Stamp not previously used (replay prevention)
## Testing
- All existing tests pass (hashcash disabled in test config with `HashcashBits: 0`)
- `docker build .` passes (lint + test + build)
<!-- session: agent:sdlc-manager:subagent:f98d712e-8a40-4013-b3d7-588cbff670f4 -->
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