add basic concord backend

Cargo.lock

@@ -1310,8 +1310,12 @@ dependencies = [
  "data-encoding",
  "hkdf",
  "nostr",
+ "nostr-memory",
  "nostr-sdk",
+ "rand 0.10.2",
+ "serde_json",
  "sha2 0.10.9",
+ "smol",
 ]
 
 [[package]]

Cargo.toml

@@ -32,6 +32,8 @@ aes-gcm = "0.10"
 sha2 = "0.10"
 data-encoding = "2"
 hkdf = "0.12"
+# Pinned to the instance `nostr-sdk` already builds, so NIP-44 nonces share it
+rand = { version = "0.10", default-features = false, features = [ "std", "sys_rng" ] }
 
 # Others
 anyhow = "1.0.44"

PLAN.md

@@ -46,7 +46,7 @@ Verified against the pinned revision (`nostr` 0.45.4 / `nostr-sdk` 0.45.2, git `
 | NIP-44 under a signer | `nip44::{encrypt, decrypt}` (already wrapped by `state::UniversalSigner`) |
 | Event id recomputation | `EventId::compute(pubkey, created_at, kind, tags, content)`, `UnsignedEvent::compute_id` |
 | Event (de)serialization | `Event::{from_json, as_json, verify}`, `UnsignedEvent::from_json` |
-| Building events | `EventBuilder::new(..).tags(..).custom_created_at(..)`, `FinalizeEvent::finalize(&Keys)` |
+| Building events | `EventBuilder::new(..).tags(..).custom_created_at(..)`, `FinalizeEvent::finalize(&Keys)`; `UnsignedEvent::new(..)` for rumors, whose tags are the author's contract and must not be normalized |
 | Tags | `Tag::{custom, identifier, public_key, expiration}`, `Tags`, `SingleLetterTag` |
 | Kinds | `Kind::GiftWrap` (1059), `Kind::Custom(21059|20013|20014|3308|…)`, `Kind::is_ephemeral` |
 | Publish | `Client::send_event(&event).to(relays).ack_policy(AckPolicy::none())` |
@@ -59,16 +59,16 @@ Verified against the pinned revision (`nostr` 0.45.4 / `nostr-sdk` 0.45.2, git `
 
 **Not needed.** `secp256k1` (use `nostr::SecretKey::from_slice` + `Keys::new`), `base64` (use `data_encoding::BASE64`, already a workspace dep), `bech32` (NIP-19 is in the SDK), any new storage engine (the client's LMDB database is enough), any new HTTP client.
 
-**Add one dependency now:** `hkdf = "0.12"` (already in `Cargo.lock` transitively). Add it to `[workspace.dependencies]` and to the new crate. `sha2` is already a workspace dep. **Two more at M8:** the Pin List's per-message key disclosure needs `chacha20 = "0.9"` (already in the tree because we enable nostr's `nip44`, which is where `chacha20` comes from) and `hmac = "0.12"` (already in the tree via `hkdf`) — see §14.8. Zero new crates, all three are direct-dependency lines only.
+**Dependencies added so far:** `hkdf = "0.12"` at M0 (already in `Cargo.lock` transitively) and `rand = "0.10"` at M1 for the NIP-44 nonce, pinned to the exact instance `nostr` already builds (`default-features = false`, features `std` + `sys_rng`) so `nostr`'s `os-rng` and ours unify on one `rand`/`getrandom`. `sha2` and `data-encoding` were already workspace deps. **Two more at M8:** the Pin List's per-message key disclosure needs `chacha20 = "0.9"` (already in the tree because we enable nostr's `nip44`, which is where `chacha20` comes from) and `hmac = "0.12"` (already in the tree via `hkdf`) — see §14.8. Zero new crates so far, and all of these are direct-dependency lines only.
 
 **Why not depend on Vector's crates.** `vector-core` (published, MIT) holds the only other Rust Concord implementation, in `src/community/v2/*`. It is not reusable as a dependency, and the "reuse their crypto" argument does not hold:
 
 - **No shared types.** It exact-pins the nostr family (`nostr = "=0.45.1"`, `nostr-sdk = "=0.45.1"`, `nostr-connect = "=0.45.1"`, `nostr-blossom = "=0.45.0"`) with the note that a caret range would let a consumer resolve a mixed set, while we track git master (`b230cec`, 0.45.4 / 0.45.2). A registry 0.45.1 and a git 0.45.4 cannot unify, so a build linking both carries two `nostr` crates whose `Event`/`Keys`/`PublicKey`/`Client` are unrelated types.
 - **Not wasm-buildable.** `rusqlite` (bundled C SQLite), `libc`, `rustls`, `reqwest`, `image`, `bip39`, and a `tokio` `net` + `rt-multi-thread` requirement; `VectorCore::init` installs a process-global rustls provider and raises the fd limit. Coop's `web` target is wasm32.
 - **It is an application core, not a Concord library.** 80k+ lines over 111 files, built on process-global singletons (`state::STATE`, `MY_SECRET_KEY`, one app-data dir, one live account, `traits::set_event_emitter`) and its own SQLite schema, relay pool and blocking `listen()` loop. Adopting it means handing it the nsec and letting it own the client, the database and the event loop — replacing `state`, `chat` and `person` rather than reusing a component. Its `login` stores raw secret-key bytes in that global vault, so an account whose key lives in a signer cannot drive it.
-- **There is no cryptography to share.** Both implementations call the same audited crates — `hkdf`, `sha2`, nostr's secp256k1 keypair, and nostr's NIP-44 v2. Vector's comment on that same dependency is "audited RustCrypto crate rather than a hand-rolled construction". Our `derive.rs` has no curve arithmetic, AEAD or randomness of its own: it holds the frozen `info` layout and label table, which are the wire format, not a primitive.
+- **There is no cryptography to share.** Both implementations call the same audited crates — `hkdf`, `sha2`, nostr's secp256k1 keypair, and nostr's NIP-44 v2. Vector's comment on that same dependency is "audited RustCrypto crate rather than a hand-rolled construction". Confirmed in M1 by reading `community/cipher.rs`: it is a ~20-line wrapper that draws an OS nonce, calls `nostr::nip44::v2::encrypt_to_bytes_with_nonce`, and base64s the result — which is precisely what `stream.rs` does. Their `stream.rs` likewise calls `nostr_sdk::prelude::nip44::v2::{decrypt_to_bytes, ConversationKey}` directly. Our `derive.rs` holds the frozen `info` layout and label table, and `stream.rs` the seal/wrap ordering; both are wire format, not primitives.
 
-So Vector's crates earn their place as an **oracle, not a dependency**: the golden vectors in `derive.rs` are their published data, produced by an independent implementation.
+So Vector's crates earn their place as an **oracle, not a dependency**: the golden vectors in `derive.rs` are their published data, and their `community/v2/stream.rs` was diffed against our §7 before the codec was written. It agrees on every wire detail, and contributed the `ms` first-wins rule, the Control Plane's no-`ms` rumor shape and the `rewrap_seal` contract.
 
 ## 4. Crate layout
 
@@ -91,7 +91,9 @@ crates/concord/
 
 `Community` and `Channel` GPUI entities live in `src/lib.rs` next to the registry — they are the public surface, not a separate concern. Ten modules, each with real content; no single-fn files.
 
-Dependencies: `common`, `state`, `person`, `device`, `settings`, `gpui`, `nostr` (for `nip44` features), `nostr-sdk`, `hkdf`, `sha2`, `serde`, `serde_json`, `anyhow`, `flume`, `smallvec`, `itertools`, `futures`, `log`, `instant`. Everything under `cfg(not(target_arch = "wasm32"))` follows the `chat`/`state` split so the crate still builds for web.
+Dependencies: `common`, `state`, `person`, `device`, `settings`, `gpui`, `nostr` (for `nip44` features), `nostr-sdk`, `hkdf`, `sha2`, `data-encoding`, `rand`, `serde`, `serde_json`, `anyhow`, `flume`, `smallvec`, `itertools`, `futures`, `log`, `instant`. Everything under `cfg(not(target_arch = "wasm32"))` follows the `chat`/`state` split so the crate still builds for web.
+
+Declare only what a milestone actually uses. As of M1 the crate depends on `nostr`, `nostr-sdk`, `hkdf`, `sha2`, `data-encoding`, `rand`, `anyhow` (plus `nostr-memory`, `serde_json`, `smol` for tests). `rand` is pinned to the `0.10.2` instance `nostr` already builds and shares its `getrandom`, which the `web` crate already enables `wasm_js` on — so no new package and no new wasm obligation.
 
 ## 5. Core types
 
@@ -185,7 +187,7 @@ Rules that must be enforced by construction, not by convention:
 
 **Golden vectors.** `derive.rs` pins all 18 published vectors (the seed and `pk` for channel, control, control-signer and guestbook; both keyed labels at epoch `0` and at `0x0102030405060708`; both rekey labels at epoch 1; dissolved; all four locators; the invite key; the community id; the epoch-key commitment), cross-checked against an independent Python implementation (RFC 5869 HKDF plus pure-integer secp256k1) before being frozen. One vector is missing upstream — `pins_locator` — so we mint it from our own implementation and pin it, flagged in the test as self-referential. Changing any pinned value means the wire format changed.
 
-## 7. Stream codec (`stream.rs`)
+## 7. Stream codec (`stream.rs`) — implemented in M1
 
 ```rust
 pub const KIND_WRAP: u16 = 1059;
@@ -194,29 +196,56 @@ pub const KIND_SEAL_ENCRYPTED: u16 = 20013;
 pub const KIND_SEAL_PLAINTEXT: u16 = 20014;
 pub const NIP44_MAX_PLAINTEXT: usize = 65_535;
 
+pub enum SealForm { Encrypted, Plaintext }
+
+pub struct OpenedStream {
+    pub rumor_id: EventId,
+    pub author: PublicKey,
+    pub seal_form: SealForm,
+    pub seal: Event,
+    pub wrapper_id: EventId,
+    pub at_ms: u64,
+    pub rumor: UnsignedEvent,
+}
+
+pub fn split_ms(at_ms: u64) -> (u64, u16);
+pub fn resolve_ms_strict(rumor: &UnsignedEvent) -> Result<u64, StreamError>;
+
 pub fn seal_content(rumor: &UnsignedEvent, form: SealForm, group: &GroupKey) -> Result<String, StreamError>;
 pub fn build_seal(rumor: &UnsignedEvent, form: SealForm, group: &GroupKey, author: &Keys) -> Result<Event, StreamError>;
 pub fn wrap_seal(seal: &Event, group: &GroupKey, wrap_kind: u16, at: Timestamp, extra: &[Tag]) -> Result<(Event, Keys), StreamError>;
+pub fn rewrap_seal(seal: &Event, new_group: &GroupKey, at: Timestamp) -> Result<(Event, Keys), StreamError>;
 
 pub fn open_wrap(wrap: &Event, group: &GroupKey) -> Result<OpenedStream, StreamError>;
-pub fn open_wrap_at(wrap: &Event, address: &PublicKey, conversation: &ConversationKey, verify_wrap_sig: bool) -> Result<OpenedStream, StreamError>;
+pub fn open_wrap_at(wrap: &Event, address: &PublicKey, conversation: &ConversationKey, verify_wrap_signature: bool) -> Result<OpenedStream, StreamError>;
+
+pub fn build_rumor_ms(kind: u16, author: PublicKey, content: &str, tags: Vec<Tag>, at_ms: u64) -> UnsignedEvent;
+pub fn build_rumor_secs(kind: u16, author: PublicKey, content: &str, tags: Vec<Tag>, at_secs: u64) -> UnsignedEvent;
 
 pub fn channel_binding_tags(channel: &ChannelId, epoch: Epoch) -> Vec<Tag>;
 pub fn check_channel_binding(rumor: &UnsignedEvent, channel: &ChannelId, epoch: Epoch) -> Result<(), StreamError>;
-pub fn build_rumor(kind: u16, author: PublicKey, content: &str, tags: Vec<Tag>, at_ms: u64) -> UnsignedEvent;  // appends ["ms", n]
-pub fn resolve_ms_strict(rumor: &UnsignedEvent) -> Result<u64, StreamError>;
 ```
 
+`StreamError` is a typed enum, not `anyhow`: the caller has to tell a drop from a fatal, and M1's acceptance criterion is that rejections happen in the documented order.
+
+Refinements against the draft this plan opened with, decided after diffing Vector's `crates/vector-core/src/community/v2/stream.rs` (Concord has no crate of its own there, and `envelope.rs` does not exist):
+
+- `build_rumor` became `build_rumor_ms` plus `build_rumor_secs`. The Control Plane edition carries **no** `ms` tag, because editions fold by version, not by time.
+- `rewrap_seal` was added to the codec. Without it the plaintext-seal carry-forward has no expression, and M7's compaction is its only caller.
+- NIP-44 is reached through `nostr`'s own `nip44::v2::{encrypt_to_bytes_with_nonce, decrypt_to_bytes, ConversationKey}`, with a fresh OS nonce per message and `data_encoding::BASE64` for carriage. This is exactly what Vector does; there is no cryptography of theirs to reuse.
+
 Design points that are easy to get wrong:
 
 - The wrap is signed by the **stream key** with a random ephemeral `p` tag — NIP-59 reversed. `extra` is how the caller mirrors a NIP-40 expiration onto the wrap.
 - The seal is signed by the **real author** and carries `created_at` equal to the rumor's. It is never published bare.
 - Control plane **must** use the plaintext seal; chat, guestbook and rekey planes **must** use the encrypted one. Each plane asserts its own form at both ends.
 - The control plane is a write-restricted stream: the wrap key derives from `control_root` while the content is encrypted under the `community_root`-derived conversation key. `open_wrap_at` takes the two halves separately for this reason.
-- Open order: kind → address match → wrap signature (only when `verify_wrap_sig`) → NIP-44 open → seal kind → seal signature → rumor parse → `rumor.pubkey == seal.pubkey` → recompute the rumor id and reject a mismatch → strict `ms` resolve.
+- Open order: kind → address match → wrap signature (only when `verify_wrap_signature`) → NIP-44 open → seal kind → seal signature → rumor parse → `rumor.pubkey == seal.pubkey` → recompute the rumor id and reject a mismatch → strict `ms` resolve.
 - Enforce the 65 535-byte NIP-44 cap at every nesting layer before publishing.
 - Do not verify the wrap signature for ordinary planes: every reader holds the group key, so the signature proves nothing. It matters only for the restricted control plane and for rekeys.
 - The ephemeral wrap keypair is returned to the caller so a client may NIP-09-scrub its own wrap later.
+- **A duplicate `ms` tag takes the first value; it is not rejected.** Rejecting made Vector and Armada disagree on whether the event *exists*, and because `ms` orders messages that divergence reached membership. `ms` is the publisher's own value, so conceding a second tag grants an attacker no reach a single one did not. A present-but-valueless `ms`, or one that is not a lone canonical decimal in `0..=999`, is `BadMs` and the event is dropped, never clamped — `u64::from_str` alone would accept a leading `+`, a second encoding a strict peer rejects, so the digit check comes first.
+- A binding tag that names the same key twice is rejected outright, since first-match would then be the reader's choice rather than the author's; a valueless tag counts as absent, so a true absence reports `MissingTag`.
 
 ## 8. Planes, state and folds
 
@@ -373,14 +402,26 @@ pub fn compact(fold, epoch, new_control_root, ...) -> Vec<Event>;   // re-wrap h
 
 Dissolution (CORD-02 §9) also lives here: a chainless, owner-signed `vsk 10` tombstone at `dissolved_group_key(id)`, plaintext-sealed, and a verifier **must** refuse any tombstone whose `eid` is not the community's own id (including the all-zero placeholder — accepting it lets an owner's genuine tombstone for one community be re-wrapped at another of theirs and kill it permanently). On sight the community is sealed read-only: subscriptions halt, nothing new is honored, existing history stays readable, and a member's delete of their own message is still honored.
 
-## 9. Storage (`store.rs`)
+## 9. Storage (`store.rs`) — local layer implemented in M1
 
 Three layers, no new storage engine:
 
 1. **Raw wraps** (kind 1059) are persisted automatically by the SDK's relay pool when a subscription or fetch matches a filter. Nothing to write.
 2. **Opened rumors** are cached locally as NIP-78 `Kind::ApplicationSpecificData` events signed by a session-local keypair, exactly like `chat::set_rumor`. Tags: `["d", rumor_id]` (replace key), `["c", channel_hex]`, `["p", author]`, `["k", kind]`, `["e", wrap_id]`, `["t", "concord"]`. Contents are the rumor JSON.
    - The `c`/`t` keys deliberately differ from chat's `r` key so the two message namespaces can never collide in one database.
-   - The read path dedupes by rumor id and keeps the newest `created_at`, because the local signing key changes per session.
+   - `created_at` is the **message's own second** (from `at_ms`), not the wall clock. Otherwise `until` and the ordering would page on cache time rather than message time.
+   - The read path dedupes by rumor id and keeps the newest `created_at`, because the local signing key changes per session and each session leaves its own copy. The query therefore carries no filter `limit` — every copy has to be in hand before they can be collapsed — and the cap is applied to the deduplicated result instead.
+   - The layer takes `&dyn NostrDatabase`, not `&Client`: it is local-only, which keeps it testable without a relay or a GPUI context.
+
+```rust
+pub async fn cache_rumor(database: &dyn NostrDatabase, channel: &ChannelId, opened: &OpenedStream) -> Result<()>;
+pub async fn query_rumors(database: &dyn NostrDatabase, channel: &ChannelId, until: Option<Timestamp>, limit: usize) -> Result<Vec<UnsignedEvent>>;
+```
+
+`query_rumors` returns `UnsignedEvent`, not `Event`: the cached payload *is* a rumor, which is also what `OpenedStream` carries, so the caller never has to re-parse.
+
+**Deferred to M4:** the relay-paging `backfill`. It is network history paging whose "step past the same-second wall" policy belongs with the sync engine, and M1 has no subscription to test it against.
+
 3. **Community state** — one local document per community, `Kind::ApplicationSpecificData` with `["d", "concord/<community_id>"]`:
 
 ```rust
@@ -404,19 +445,10 @@ pub struct CommunityState {
 }
 ```
 
-Writes are debounced (a fold head changes on every edition); reads load once at init.
+Writes are debounced (a fold head changes on every edition); reads load once at init. This layer lands in M2, once `Community` exists to hold it.
 
 **Decision, stated for the record:** this document stores raw community keys unencrypted in a plaintext local database. That matches the existing posture — `chat` already caches decrypted message rumors in the same LMDB. If that posture ever changes, the state document is the one to wrap with NIP-44-to-self, since it is the only local artifact holding keys.
 
-History queries:
-
-```rust
-pub async fn query_messages(&self, channel: &ChannelId, until: Option<Timestamp>, limit: usize) -> Result<Vec<Event>, Error>;
-pub async fn backfill(&self, plane_authors: &[PublicKey], relays: &[RelayUrl], until: Option<Timestamp>, limit: usize) -> Result<Vec<Event>, Error>;
-```
-
-`query_messages` reads the local cache (`Filter::new().kind(ApplicationSpecificData).custom_tag(LOWERCASE_C, channel_hex)`); `backfill` pages relays newest-first with `until`, deduplicating by wrap id and stepping past same-second walls.
-
 ## 10. Sync engine and GPUI conventions
 
 `ConcordRegistry` mirrors `ChatRegistry`'s shape exactly: a foreground GPUI entity holding `Entity<Community>` handles, a `flume` signal bus, one background notification listener, one foreground consumer, and task slots that are cleared when the signer changes.
@@ -537,7 +569,7 @@ pub fn pin(&self, id: EventId, cx: &App) -> Task<Result<(), Error>>; // vsk 11,
 
 ## 11. Integration with existing crates
 
-1. **`crates/chat/src/lib.rs` — required fix.** `handle_notifications` currently treats *every* kind 1059 event as a NIP-17 wrap for the current user and pushes an unwrap failure into the trash. Concord wraps are kind 1059 with an ephemeral `p` tag, so they would flood the trash and leak error toasts. Route by `subscription_id` from `RelayMessage::Event` against `sub_id1`/`sub_id2`, and drop the `if rumor.tags.is_empty()` heuristic once the real recipient check is in place.
+1. **`crates/chat/src/lib.rs` — required fix, applied in M2.** `handle_notifications` currently treats *every* kind 1059 event as a NIP-59 gift wrap for the current user and pushes an unwrap failure into the trash. Concord wraps are kind 1059 with an ephemeral `p` tag, so they would flood the trash and leak error toasts. Route by `subscription_id` from `RelayMessage::Event` against `sub_id1`/`sub_id2`, and drop the `if rumor.tags.is_empty()` recipient heuristic. M1 did not need it because nothing subscribes yet.
 2. **`desktop/src/main.rs` and `web/src/lib.rs`** — add `concord::init(window, cx)` after `chat::init(window, cx)`.
 3. **`Cargo.toml`** — add `hkdf = "0.12"` to `[workspace.dependencies]`; add the crate to `desktop` and `web` dependencies. No other workspace changes.
 4. **No changes** to `state`, `person`, `device`, `settings`, `common`, or `ui`.
@@ -550,7 +582,7 @@ Each of these has burned a real implementation, or is a documented cross-client
 - Require `rumor.pubkey == seal.pubkey`.
 - Require the plaintext seal form on Control and the encrypted form on Chat/Guestbook/Rekey — a strict reader must drop a mis-sealed edition rather than fold a chain a later compaction would fork.
 - Check `channel` **and** `epoch` against the plane whose key opened the wrap; reject duplicates of either tag.
-- Reject duplicate `vsk`/`eid`/`ev`/`ep`/`vac` tags; require decimal-with-no-leading-zeros on every numeric tag.
+- Reject duplicate `vsk`/`eid`/`ev`/`ep`/`vac` tags; require decimal-with-no-leading-zeros on every numeric tag. The one exception is `ms`, which takes its first value rather than erroring — see §7 for why rejecting it reached membership.
 - Refuse a tombstone whose `eid` is not this community's id.
 - Adopt a `control_root` from a Grant only if it derives to the `control_pk` held for that epoch; adopt a rekey blob only if its bound plaintext matches the scope and epoch and its `prevcommit` matches the key currently held.
 - Never conclude removal from a partial rekey chunk set.
@@ -564,11 +596,11 @@ Each of these has burned a real implementation, or is a documented cross-client
 
 | # | Deliverable | Done when |
 | --- | --- | --- |
-| M0 | Crate skeleton, `derive.rs`, golden vectors, workspace wiring | `cargo test -p concord` pins every derivation from an independent vector set; all labels match Appendix A.6 |
-| M1 | `stream.rs` + `store.rs` | seal/wrap/open round-trips for both seal forms; malformed inputs rejected in the documented order; local cache reads back after a restart |
+| M0 | Crate skeleton, `derive.rs`, golden vectors, workspace wiring | ✅ `cargo test -p concord` pins every derivation; all labels match Appendix A.6 |
+| M1 | `stream.rs` + `store.rs` | ✅ seal/wrap/open round-trips for both seal forms; hostile wraps rejected in the documented order; the local cache reads back with the group key gone |
 | M2 | `edition.rs` + `control.rs` genesis | a community is created and published; its two genesis wraps open at a second client sharing the keys; edition hash matches the cross-client vector |
 | M3 | Control fold + roster + metadata/channels | fold tests for chains, gaps, downgrade refusal, fork tiebreak, compaction dangle; metadata and channel edits visible to a second client |
-| M4 | Chat plane | send/receive/edit/delete/reaction across two identities; history pages backwards across an epoch boundary; binding checks reject a foreign channel/epoch |
+| M4 | Chat plane | send/receive/edit/delete/reaction across two identities; history pages backwards across an epoch boundary (relay `backfill` lands here); binding checks reject a foreign channel/epoch |
 | M5 | Guestbook + member list + moderation | join/leave/kick/ban converge to the same memberlist on both clients; every authority rule from §8.1 has a negative test |
 | M6 | Invites + Community List | link mint → fetch → join round-trips; revoked link refuses; direct invite lands in the recipient's giftwrap inbox via the `k` tag; a second device reconstructs membership from 13302 |
 | M7 | Rekeys + refounding + dissolution | a removed member stops reading after a rekey; continuity and race rules tested; a tombstone seals the community and a foreign-id tombstone is refused |
@@ -576,6 +608,8 @@ Each of these has burned a real implementation, or is a documented cross-client
 
 Ordering is deliberately dependency-first: each milestone is usable on its own, and nothing in M2+ depends on a later milestone.
 
+M1 closed with `cargo test -p concord` (5 tests), `cargo clippy -p concord --all-targets`, and `cargo fmt -p concord --check` all clean. `rand` was added to the workspace pinned to the same `0.10.2` instance `nostr` already builds, so `Cargo.lock` gained no package.
+
 ## 14. Open questions and risks
 
 1. **Community List kind.** CORD-02 §8 specifies `13302`, replaceable. Vector has retired it in favour of fragmented `33302`, because a replaceable kind holds one event per pubkey and so cannot shard past the NIP-44 size cap. We implement `13302` per spec, enforce the 50-membership cap and pre-publish size check, and treat `33302` as an interop follow-up. Confirm with Armada before writing the multi-device code.

crates/concord/Cargo.toml

@@ -11,4 +11,10 @@ nostr-sdk.workspace = true
 hkdf.workspace = true
 sha2.workspace = true
 data-encoding.workspace = true
+rand.workspace = true
 anyhow.workspace = true
+
+[dev-dependencies]
+nostr-memory.workspace = true
+serde_json.workspace = true
+smol.workspace = true

crates/concord/src/lib.rs

@@ -1,4 +1,6 @@
 pub mod derive;
+pub mod store;
+pub mod stream;
 
 use std::fmt;
 use std::str::FromStr;

crates/concord/src/store.rs

@@ -0,0 +1,156 @@
+use std::collections::BTreeMap;
+use std::sync::LazyLock;
+
+use anyhow::{Result, anyhow};
+use nostr_sdk::prelude::*;
+
+use crate::ChannelId;
+use crate::stream::OpenedStream;
+
+static LOCAL_KEYS: LazyLock<Keys> = LazyLock::new(Keys::generate);
+
+const CHANNEL_TAG: SingleLetterTag = SingleLetterTag::LOWERCASE_C;
+const MARK_TAG: SingleLetterTag = SingleLetterTag::LOWERCASE_T;
+const MARK_VALUE: &str = "concord";
+const WRAP_TAG: &str = "e";
+const KIND_TAG: &str = "k";
+
+pub async fn cache_rumor(
+    database: &dyn NostrDatabase,
+    channel: &ChannelId,
+    opened: &OpenedStream,
+) -> Result<()> {
+    let tags = vec![
+        Tag::identifier(opened.rumor_id),
+        Tag::custom(KIND_TAG, [opened.rumor.kind.to_string()]),
+        Tag::custom(WRAP_TAG, [opened.wrapper_id.to_string()]),
+        Tag::custom(MARK_TAG.as_str(), [MARK_VALUE]),
+        Tag::custom(CHANNEL_TAG.as_str(), [channel.to_hex()]),
+        Tag::public_key(opened.author),
+    ];
+    let at = Timestamp::from_secs(opened.at_ms / 1000);
+    let event = EventBuilder::new(Kind::ApplicationSpecificData, opened.rumor.as_json())
+        .tags(tags)
+        .custom_created_at(at)
+        .finalize_async(&*LOCAL_KEYS)
+        .await?;
+
+    database.save_event(&event).await?;
+
+    Ok(())
+}
+
+/// Read a channel's cached rumors.
+pub async fn query_rumors(
+    database: &dyn NostrDatabase,
+    channel: &ChannelId,
+    until: Option<Timestamp>,
+    limit: usize,
+) -> Result<Vec<UnsignedEvent>> {
+    let mut filter = Filter::new()
+        .kind(Kind::ApplicationSpecificData)
+        .custom_tag(MARK_TAG, MARK_VALUE)
+        .custom_tag(CHANNEL_TAG, channel.to_hex());
+
+    if let Some(until) = until {
+        filter = filter.until(until);
+    }
+
+    let mut newest: BTreeMap<String, Event> = BTreeMap::new();
+    for event in database.query(filter).await? {
+        let Some(rumor_id) = event.tags.identifier() else {
+            continue;
+        };
+
+        match newest.get(&rumor_id) {
+            Some(existing) if existing.created_at >= event.created_at => {}
+            _ => {
+                newest.insert(rumor_id, event);
+            }
+        }
+    }
+
+    let mut events: Vec<Event> = newest.into_values().collect();
+    events.sort_by_key(|event| std::cmp::Reverse(event.created_at));
+    events.truncate(limit);
+
+    let mut rumors = Vec::with_capacity(events.len());
+    for event in events {
+        let rumor = UnsignedEvent::from_json(event.content)
+            .map_err(|error| anyhow!("cached rumor is not a valid event: {error}"))?;
+        rumors.push(rumor);
+    }
+
+    Ok(rumors)
+}
+
+#[cfg(test)]
+mod tests {
+    use nostr_memory::MemoryDatabase;
+
+    use super::*;
+    use crate::Epoch;
+    use crate::derive::channel_group_key;
+    use crate::stream::{
+        KIND_WRAP, SealForm, build_rumor_ms, build_seal, channel_binding_tags, open_wrap, wrap_seal,
+    };
+
+    const SECRET: [u8; 32] = [0x07u8; 32];
+
+    #[test]
+    fn rumors_read_back_after_a_restart() {
+        let database = MemoryDatabase::unbounded();
+        let channel = ChannelId::from_bytes([0xabu8; 32]);
+        let author = Keys::generate();
+
+        smol::block_on(async {
+            let group = channel_group_key(&SECRET, &channel, Epoch(0)).expect("derives");
+
+            for (content, at_ms) in [("first", 1_000_000u64), ("second", 2_000_000)] {
+                let rumor = build_rumor_ms(
+                    9,
+                    author.public_key(),
+                    content,
+                    channel_binding_tags(&channel, Epoch(0)),
+                    at_ms,
+                );
+                let seal = build_seal(&rumor, SealForm::Encrypted, &group, &author).expect("seals");
+                let (wrap, _) = wrap_seal(
+                    &seal,
+                    &group,
+                    KIND_WRAP,
+                    Timestamp::from_secs(at_ms / 1000),
+                    &[],
+                )
+                .expect("wraps");
+
+                let opened = open_wrap(&wrap, &group).expect("opens");
+                cache_rumor(&database, &channel, &opened)
+                    .await
+                    .expect("caches");
+            }
+
+            // The group key is gone; only the local cache stands in for it.
+            let rumors = query_rumors(&database, &channel, None, 10)
+                .await
+                .expect("queries");
+            assert_eq!(rumors.len(), 2, "both messages come back");
+            assert_eq!(rumors[0].content, "second", "newest first");
+            assert_eq!(rumors[1].content, "first");
+
+            // A page boundary in message time, not in cache time.
+            let until = Timestamp::from_secs(1_500);
+            let page = query_rumors(&database, &channel, Some(until), 10)
+                .await
+                .expect("queries");
+            assert_eq!(page.len(), 1);
+            assert_eq!(page[0].content, "first");
+
+            let capped = query_rumors(&database, &channel, None, 1)
+                .await
+                .expect("queries");
+            assert_eq!(capped.len(), 1);
+            assert_eq!(capped[0].content, "second");
+        });
+    }
+}

crates/concord/src/stream.rs

@@ -0,0 +1,660 @@
+use std::fmt;
+
+use data_encoding::BASE64;
+use nostr::nips::nip44::v2::{ConversationKey, decrypt_to_bytes, encrypt_to_bytes_with_nonce};
+use nostr_sdk::prelude::{
+    Event, EventBuilder, EventId, FinalizeEvent, Keys, Kind, PublicKey, Tag, Timestamp,
+    UnsignedEvent,
+};
+use rand::TryRng as _;
+use rand::rngs::SysRng;
+
+use crate::derive::GroupKey;
+use crate::{ChannelId, Epoch};
+
+pub const KIND_WRAP: u16 = 1059;
+pub const KIND_WRAP_EPHEMERAL: u16 = 21059;
+pub const KIND_SEAL_ENCRYPTED: u16 = 20013;
+pub const KIND_SEAL_PLAINTEXT: u16 = 20014;
+pub const NIP44_MAX_PLAINTEXT: usize = 65_535;
+
+const TAG_MS: &str = "ms";
+const TAG_CHANNEL: &str = "channel";
+const TAG_EPOCH: &str = "epoch";
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum SealForm {
+    Encrypted,
+    Plaintext,
+}
+
+impl SealForm {
+    pub fn kind(self) -> u16 {
+        match self {
+            SealForm::Encrypted => KIND_SEAL_ENCRYPTED,
+            SealForm::Plaintext => KIND_SEAL_PLAINTEXT,
+        }
+    }
+
+    fn from_kind(kind: u16) -> Option<Self> {
+        match kind {
+            KIND_SEAL_ENCRYPTED => Some(SealForm::Encrypted),
+            KIND_SEAL_PLAINTEXT => Some(SealForm::Plaintext),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum StreamError {
+    Sign(String),
+    Encrypt(String),
+    Decrypt(String),
+    Parse(String),
+    Oversize(usize),
+    BadWrapKind(u16),
+    WrongStream,
+    BadWrapSignature,
+    BadSealKind(u16),
+    BadSealSignature,
+    AuthorMismatch,
+    BadRumorId,
+    BadMs,
+    ChannelMismatch,
+    EpochMismatch,
+    MissingTag(&'static str),
+    DuplicateTag(&'static str),
+    NotRewrappable,
+}
+
+impl fmt::Display for StreamError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            StreamError::Sign(error) => write!(f, "sign: {error}"),
+            StreamError::Encrypt(error) => write!(f, "encrypt: {error}"),
+            StreamError::Decrypt(error) => write!(f, "decrypt: {error}"),
+            StreamError::Parse(error) => write!(f, "parse: {error}"),
+            StreamError::Oversize(len) => write!(f, "plaintext {len} bytes exceeds NIP-44 cap"),
+            StreamError::BadWrapKind(kind) => write!(f, "not a wrap kind: {kind}"),
+            StreamError::WrongStream => write!(f, "wrap author is not this stream"),
+            StreamError::BadWrapSignature => write!(f, "restricted wrap signature invalid"),
+            StreamError::BadSealKind(kind) => write!(f, "not a seal kind: {kind}"),
+            StreamError::BadSealSignature => write!(f, "seal signature invalid"),
+            StreamError::AuthorMismatch => write!(f, "rumor pubkey != seal pubkey"),
+            StreamError::BadRumorId => write!(f, "rumor id != computed hash"),
+            StreamError::BadMs => write!(f, "ms is not a canonical decimal in 0..=999"),
+            StreamError::ChannelMismatch => write!(f, "channel binding mismatch"),
+            StreamError::EpochMismatch => write!(f, "epoch binding mismatch"),
+            StreamError::MissingTag(name) => write!(f, "missing rumor tag: {name}"),
+            StreamError::DuplicateTag(name) => write!(f, "duplicate rumor tag: {name}"),
+            StreamError::NotRewrappable => write!(f, "only plaintext seals survive re-wrapping"),
+        }
+    }
+}
+
+impl std::error::Error for StreamError {}
+
+#[derive(Debug, Clone)]
+pub struct OpenedStream {
+    pub rumor_id: EventId,
+    pub author: PublicKey,
+    pub seal_form: SealForm,
+    pub seal: Event,
+    pub wrapper_id: EventId,
+    pub at_ms: u64,
+    pub rumor: UnsignedEvent,
+}
+
+pub fn split_ms(at_ms: u64) -> (u64, u16) {
+    (at_ms / 1000, (at_ms % 1000) as u16)
+}
+
+/// Build a rumor carrying a full epoch-ms time: `created_at`
+/// holds the seconds and an `["ms", 0..=999]` tag the remainder.
+pub fn build_rumor_ms(
+    kind: u16,
+    author: PublicKey,
+    content: &str,
+    mut tags: Vec<Tag>,
+    at_ms: u64,
+) -> UnsignedEvent {
+    let (seconds, offset) = split_ms(at_ms);
+    tags.push(Tag::custom(TAG_MS, [offset.to_string()]));
+    build_rumor_secs(kind, author, content, tags, seconds)
+}
+
+/// Build a rumor with a plain seconds timestamp and no `ms` tag.
+pub fn build_rumor_secs(
+    kind: u16,
+    author: PublicKey,
+    content: &str,
+    tags: Vec<Tag>,
+    at_secs: u64,
+) -> UnsignedEvent {
+    let mut rumor = UnsignedEvent::new(
+        author,
+        Timestamp::from_secs(at_secs),
+        Kind::Custom(kind),
+        tags,
+        content,
+    );
+    rumor.ensure_id();
+    rumor
+}
+
+/// Resolve a rumor's true millisecond time.
+pub fn resolve_ms_strict(rumor: &UnsignedEvent) -> Result<u64, StreamError> {
+    let seconds = rumor.created_at.as_secs().saturating_mul(1000);
+    let mut tag: Option<Option<String>> = None;
+
+    for candidate in rumor.tags.iter() {
+        let fields = candidate.as_slice();
+        if fields.first().map(String::as_str) == Some(TAG_MS) {
+            tag = Some(fields.get(1).cloned());
+            break;
+        }
+    }
+
+    let Some(raw) = tag else {
+        return Ok(seconds);
+    };
+    let raw = raw.ok_or(StreamError::BadMs)?;
+
+    if raw.is_empty() || !raw.bytes().all(|byte| byte.is_ascii_digit()) {
+        return Err(StreamError::BadMs);
+    }
+
+    let offset: u64 = raw.parse().map_err(|_| StreamError::BadMs)?;
+
+    if offset > 999 || (raw.len() > 1 && raw.starts_with('0')) {
+        return Err(StreamError::BadMs);
+    }
+
+    Ok(seconds.saturating_add(offset))
+}
+
+pub fn seal_content(
+    rumor: &UnsignedEvent,
+    form: SealForm,
+    group: &GroupKey,
+) -> Result<String, StreamError> {
+    let json = rumor.as_json();
+    check_plaintext_cap(json.len())?;
+
+    match form {
+        SealForm::Plaintext => Ok(json),
+        SealForm::Encrypted => Ok(BASE64.encode(&encrypt(group.conversation(), json.as_bytes())?)),
+    }
+}
+
+pub fn build_seal(
+    rumor: &UnsignedEvent,
+    form: SealForm,
+    group: &GroupKey,
+    author: &Keys,
+) -> Result<Event, StreamError> {
+    let content = seal_content(rumor, form, group)?;
+    EventBuilder::new(Kind::Custom(form.kind()), content)
+        .custom_created_at(rumor.created_at)
+        .finalize(author)
+        .map_err(|error| StreamError::Sign(error.to_string()))
+}
+
+pub fn wrap_seal(
+    seal: &Event,
+    group: &GroupKey,
+    wrap_kind: u16,
+    at: Timestamp,
+    extra: &[Tag],
+) -> Result<(Event, Keys), StreamError> {
+    if wrap_kind != KIND_WRAP && wrap_kind != KIND_WRAP_EPHEMERAL {
+        return Err(StreamError::BadWrapKind(wrap_kind));
+    }
+
+    let json = seal.as_json();
+    check_plaintext_cap(json.len())?;
+
+    let content = BASE64.encode(&encrypt(group.conversation(), json.as_bytes())?);
+    let ephemeral = Keys::generate();
+
+    let mut tags = vec![Tag::public_key(ephemeral.public_key())];
+    tags.extend_from_slice(extra);
+
+    let wrap = EventBuilder::new(Kind::Custom(wrap_kind), content)
+        .tags(tags)
+        .custom_created_at(at)
+        .finalize(group.keys())
+        .map_err(|error| StreamError::Sign(error.to_string()))?;
+
+    Ok((wrap, ephemeral))
+}
+
+pub fn rewrap_seal(
+    seal: &Event,
+    new_group: &GroupKey,
+    at: Timestamp,
+) -> Result<(Event, Keys), StreamError> {
+    if seal.kind.as_u16() != KIND_SEAL_PLAINTEXT {
+        return Err(StreamError::NotRewrappable);
+    }
+    wrap_seal(seal, new_group, KIND_WRAP, at, &[])
+}
+
+pub fn open_wrap(wrap: &Event, group: &GroupKey) -> Result<OpenedStream, StreamError> {
+    open_wrap_at(wrap, &group.pk(), group.conversation(), false)
+}
+
+/// Open and verify a wrap against a stream read view: the address to check and
+/// the conversation key that opens the wraps, with no signing secret required.
+pub fn open_wrap_at(
+    wrap: &Event,
+    address: &PublicKey,
+    conversation: &ConversationKey,
+    verify_wrap_signature: bool,
+) -> Result<OpenedStream, StreamError> {
+    let wrap_kind = wrap.kind.as_u16();
+
+    if wrap_kind != KIND_WRAP && wrap_kind != KIND_WRAP_EPHEMERAL {
+        return Err(StreamError::BadWrapKind(wrap_kind));
+    }
+
+    if wrap.pubkey != *address {
+        return Err(StreamError::WrongStream);
+    }
+
+    if verify_wrap_signature && wrap.verify().is_err() {
+        return Err(StreamError::BadWrapSignature);
+    }
+
+    let seal: Event = Event::from_json(decode_content(conversation, &wrap.content)?)
+        .map_err(|error| StreamError::Parse(error.to_string()))?;
+    let seal_kind = seal.kind.as_u16();
+    let seal_form = SealForm::from_kind(seal_kind).ok_or(StreamError::BadSealKind(seal_kind))?;
+    seal.verify().map_err(|_| StreamError::BadSealSignature)?;
+
+    let rumor_json = match seal_form {
+        SealForm::Plaintext => seal.content.clone(),
+        SealForm::Encrypted => decode_content(conversation, &seal.content)?,
+    };
+
+    let mut rumor: UnsignedEvent = UnsignedEvent::from_json(rumor_json.as_bytes())
+        .map_err(|error| StreamError::Parse(error.to_string()))?;
+
+    if rumor.pubkey != seal.pubkey {
+        return Err(StreamError::AuthorMismatch);
+    }
+
+    let computed = rumor.compute_id();
+    if let Some(claimed) = rumor.id
+        && claimed != computed
+    {
+        return Err(StreamError::BadRumorId);
+    }
+    rumor.id = Some(computed);
+
+    let at_ms = resolve_ms_strict(&rumor)?;
+
+    Ok(OpenedStream {
+        rumor_id: computed,
+        author: seal.pubkey,
+        seal_form,
+        seal,
+        wrapper_id: wrap.id,
+        at_ms,
+        rumor,
+    })
+}
+
+pub fn channel_binding_tags(channel: &ChannelId, epoch: Epoch) -> Vec<Tag> {
+    vec![
+        Tag::custom(TAG_CHANNEL, [channel.to_hex()]),
+        Tag::custom(TAG_EPOCH, [epoch.0.to_string()]),
+    ]
+}
+
+pub fn check_channel_binding(
+    rumor: &UnsignedEvent,
+    channel: &ChannelId,
+    epoch: Epoch,
+) -> Result<(), StreamError> {
+    match unique_tag(rumor, TAG_CHANNEL)? {
+        Some(value) if value == channel.to_hex() => {}
+        Some(_) => return Err(StreamError::ChannelMismatch),
+        None => return Err(StreamError::MissingTag(TAG_CHANNEL)),
+    }
+
+    match unique_tag(rumor, TAG_EPOCH)? {
+        Some(value) if value == epoch.0.to_string() => {}
+        Some(_) => return Err(StreamError::EpochMismatch),
+        None => return Err(StreamError::MissingTag(TAG_EPOCH)),
+    }
+
+    Ok(())
+}
+
+fn encrypt(conversation: &ConversationKey, plaintext: &[u8]) -> Result<Vec<u8>, StreamError> {
+    let mut nonce = [0u8; 32];
+
+    SysRng
+        .try_fill_bytes(&mut nonce)
+        .map_err(|error| StreamError::Encrypt(error.to_string()))?;
+
+    encrypt_to_bytes_with_nonce(conversation, plaintext, nonce)
+        .map_err(|error| StreamError::Encrypt(error.to_string()))
+}
+
+fn decode_content(conversation: &ConversationKey, content: &str) -> Result<String, StreamError> {
+    let payload = BASE64
+        .decode(content.as_bytes())
+        .map_err(|error| StreamError::Decrypt(error.to_string()))?;
+
+    let plaintext = decrypt_to_bytes(conversation, &payload)
+        .map_err(|error| StreamError::Decrypt(error.to_string()))?;
+
+    String::from_utf8(plaintext).map_err(|error| StreamError::Parse(error.to_string()))
+}
+
+fn check_plaintext_cap(len: usize) -> Result<(), StreamError> {
+    if len > NIP44_MAX_PLAINTEXT {
+        return Err(StreamError::Oversize(len));
+    }
+
+    Ok(())
+}
+
+fn unique_tag(rumor: &UnsignedEvent, name: &'static str) -> Result<Option<String>, StreamError> {
+    let mut found: Option<String> = None;
+
+    for tag in rumor.tags.iter() {
+        let fields = tag.as_slice();
+        if fields.len() >= 2 && fields[0] == name {
+            if found.is_some() {
+                return Err(StreamError::DuplicateTag(name));
+            }
+            found = Some(fields[1].clone());
+        }
+    }
+
+    Ok(found)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::derive::channel_group_key;
+
+    const SECRET: [u8; 32] = [0x07u8; 32];
+    const OTHER_SECRET: [u8; 32] = [0x08u8; 32];
+
+    fn channel() -> ChannelId {
+        ChannelId::from_bytes([0xabu8; 32])
+    }
+
+    fn group(epoch: u64) -> GroupKey {
+        channel_group_key(&SECRET, &channel(), Epoch(epoch)).expect("derives")
+    }
+
+    fn wrapper_p_tag(wrap: &Event) -> Option<String> {
+        wrap.tags
+            .iter()
+            .find(|tag| tag.as_slice().first().map(String::as_str) == Some("p"))
+            .and_then(|tag| tag.as_slice().get(1).cloned())
+    }
+
+    fn bound_rumor(content: &str, author: PublicKey, at_ms: u64) -> UnsignedEvent {
+        build_rumor_ms(
+            9,
+            author,
+            content,
+            channel_binding_tags(&channel(), Epoch(0)),
+            at_ms,
+        )
+    }
+
+    fn sealed(rumor: &UnsignedEvent, form: SealForm, author: &Keys) -> Event {
+        build_seal(rumor, form, &group(0), author).expect("seals")
+    }
+
+    fn wrapped(seal: &Event, kind: u16, at_secs: u64) -> Event {
+        wrap_seal(seal, &group(0), kind, Timestamp::from_secs(at_secs), &[])
+            .expect("wraps")
+            .0
+    }
+
+    fn encrypted_wrap(content: &str, author: &Keys, at_ms: u64, kind: u16) -> Event {
+        let rumor = bound_rumor(content, author.public_key(), at_ms);
+        wrapped(
+            &sealed(&rumor, SealForm::Encrypted, author),
+            kind,
+            at_ms / 1000,
+        )
+    }
+
+    #[test]
+    fn both_seal_forms_round_trip() {
+        let author = Keys::generate();
+        let at_ms = 1_686_840_217_417;
+        let wrap = encrypted_wrap("Hey chat!", &author, at_ms, KIND_WRAP);
+
+        assert_eq!(wrap.kind, Kind::GiftWrap, "the durable wrap is kind 1059");
+        assert_eq!(wrap.pubkey, group(0).pk(), "the stream key signs the wrap");
+
+        let opened = open_wrap(&wrap, &group(0)).expect("opens");
+        assert_eq!(opened.author, author.public_key());
+        assert_eq!(opened.rumor.content, "Hey chat!");
+        assert_eq!(opened.rumor_id, opened.rumor.id.expect("id is set"));
+        assert_eq!(opened.wrapper_id, wrap.id);
+        assert_eq!(opened.at_ms, at_ms);
+        assert_eq!(opened.seal_form, SealForm::Encrypted);
+        check_channel_binding(&opened.rumor, &channel(), Epoch(0)).expect("binding holds");
+
+        // The wrap's `p` tag must identify neither the stream nor the author.
+        let p = wrapper_p_tag(&wrap).expect("the wrap carries a p tag");
+        assert_ne!(p, group(0).pk_hex());
+        assert_ne!(p, author.public_key().to_hex());
+
+        // Ephemeral actions ride the same structure at a kind relays must drop.
+        let typing = encrypted_wrap("typing", &author, 5_000, KIND_WRAP_EPHEMERAL);
+        assert_eq!(typing.kind.as_u16(), 21059);
+        assert_eq!(
+            open_wrap(&typing, &group(0)).expect("opens").rumor.content,
+            "typing"
+        );
+
+        // The plaintext form carries the rumor's bytes verbatim, which is what
+        // lets a compaction re-wrap the signed edition into a later epoch.
+        let edition = build_rumor_secs(
+            3308,
+            author.public_key(),
+            "an edition",
+            vec![],
+            1_700_000_000,
+        );
+        let seal = sealed(&edition, SealForm::Plaintext, &author);
+        assert_eq!(seal.content, edition.as_json(), "the rumor rides verbatim");
+
+        let opened = open_wrap(&wrapped(&seal, KIND_WRAP, 1), &group(0)).expect("opens");
+        assert_eq!(opened.seal_form, SealForm::Plaintext);
+
+        let (rewrapped, _) =
+            rewrap_seal(&opened.seal, &group(1), Timestamp::from_secs(2)).expect("rewraps");
+        let reopened = open_wrap(&rewrapped, &group(1)).expect("opens");
+        assert_eq!(reopened.rumor_id, opened.rumor_id, "the rumor id survives");
+        assert_eq!(reopened.author, author.public_key());
+        assert_eq!(
+            reopened.seal.sig, opened.seal.sig,
+            "the signature rides whole"
+        );
+        assert_ne!(reopened.wrapper_id, opened.wrapper_id);
+
+        assert!(matches!(
+            rewrap_seal(
+                &sealed(&edition, SealForm::Encrypted, &author),
+                &group(1),
+                Timestamp::from_secs(2)
+            ),
+            Err(StreamError::NotRewrappable)
+        ));
+    }
+
+    #[test]
+    fn hostile_wraps_are_dropped_in_order() {
+        let author = Keys::generate();
+        let impostor = Keys::generate();
+
+        // Kind and address are settled before any decryption is attempted.
+        let mut wrong_kind = encrypted_wrap("x", &author, 1_000, KIND_WRAP);
+        wrong_kind.kind = Kind::Custom(1058);
+        assert!(matches!(
+            open_wrap(&wrong_kind, &group(0)),
+            Err(StreamError::BadWrapKind(1058))
+        ));
+
+        let foreign = channel_group_key(&OTHER_SECRET, &channel(), Epoch(0)).expect("derives");
+        let wrap = encrypted_wrap("x", &author, 1_000, KIND_WRAP);
+        assert!(matches!(
+            open_wrap(&wrap, &foreign),
+            Err(StreamError::WrongStream)
+        ));
+
+        // A flipped ciphertext byte fails the NIP-44 MAC.
+        let mut payload = BASE64
+            .decode(wrap.content.as_bytes())
+            .expect("content is base64");
+        payload[40] ^= 0x01;
+        let mut tampered = wrap.clone();
+        tampered.content = BASE64.encode(&payload);
+        assert!(matches!(
+            open_wrap(&tampered, &group(0)),
+            Err(StreamError::Decrypt(_))
+        ));
+
+        // A seal claiming an author it holds no signature for.
+        let seal = sealed(
+            &bound_rumor("spoof", author.public_key(), 1_000),
+            SealForm::Encrypted,
+            &impostor,
+        );
+        let mut swapped: serde_json::Value = serde_json::from_str(&seal.as_json()).expect("json");
+        swapped["pubkey"] = serde_json::Value::String(author.public_key().to_hex());
+        let seal = Event::from_json(swapped.to_string()).expect("a swapped pubkey still parses");
+        assert!(matches!(
+            open_wrap(&wrapped(&seal, KIND_WRAP, 1), &group(0)),
+            Err(StreamError::BadSealSignature)
+        ));
+
+        // A seal that does not vouch for the rumor's author.
+        let seal = sealed(
+            &bound_rumor("spoof", impostor.public_key(), 1_000),
+            SealForm::Encrypted,
+            &author,
+        );
+        assert!(matches!(
+            open_wrap(&wrapped(&seal, KIND_WRAP, 1), &group(0)),
+            Err(StreamError::AuthorMismatch)
+        ));
+
+        // A claimed id the rumor's own bytes do not hash to. The plaintext seal
+        // smuggles the forgery through verbatim.
+        let rumor = bound_rumor("real", author.public_key(), 1_000);
+        let mut forged: serde_json::Value = serde_json::from_str(&rumor.as_json()).expect("json");
+        forged["id"] = serde_json::Value::String("00".repeat(32));
+        let seal = EventBuilder::new(Kind::Custom(KIND_SEAL_PLAINTEXT), forged.to_string())
+            .custom_created_at(rumor.created_at)
+            .finalize(&author)
+            .expect("seals");
+        assert!(matches!(
+            open_wrap(&wrapped(&seal, KIND_WRAP, 1), &group(0)),
+            Err(StreamError::BadRumorId)
+        ));
+
+        // Binding splices: another channel, another epoch, a duplicate or none.
+        let doubled = vec![channel_binding_tags(&channel(), Epoch(0)); 2].concat();
+        let rumor = bound_rumor("x", author.public_key(), 1_000);
+
+        assert!(matches!(
+            check_channel_binding(&rumor, &ChannelId::from_bytes([0xcdu8; 32]), Epoch(0)),
+            Err(StreamError::ChannelMismatch)
+        ));
+
+        assert!(matches!(
+            check_channel_binding(&rumor, &channel(), Epoch(1)),
+            Err(StreamError::EpochMismatch)
+        ));
+
+        let duplicate = build_rumor_ms(9, author.public_key(), "x", doubled, 1_000);
+        assert!(matches!(
+            check_channel_binding(&duplicate, &channel(), Epoch(0)),
+            Err(StreamError::DuplicateTag(_))
+        ));
+
+        let unbound = build_rumor_ms(9, author.public_key(), "x", vec![], 1_000);
+        assert!(matches!(
+            check_channel_binding(&unbound, &channel(), Epoch(0)),
+            Err(StreamError::MissingTag(_))
+        ));
+
+        let oversize = build_rumor_ms(
+            9,
+            author.public_key(),
+            &"x".repeat(NIP44_MAX_PLAINTEXT + 1),
+            vec![],
+            1_000,
+        );
+        assert!(matches!(
+            seal_content(&oversize, SealForm::Encrypted, &group(0)),
+            Err(StreamError::Oversize(_))
+        ));
+    }
+
+    #[test]
+    fn ms_is_a_drop_gate() {
+        let author = Keys::generate();
+
+        let absent = build_rumor_secs(9, author.public_key(), "x", vec![], 1_000);
+        assert_eq!(resolve_ms_strict(&absent).expect("resolves"), 1_000_000);
+
+        let highest = build_rumor_ms(9, author.public_key(), "x", vec![], 1_000_999);
+        assert_eq!(resolve_ms_strict(&highest).expect("resolves"), 1_000_999);
+
+        for malformed in ["1000", "007", "abc", "+5", ""] {
+            let rumor = build_rumor_secs(
+                9,
+                author.public_key(),
+                "x",
+                vec![Tag::custom(TAG_MS, [malformed.to_string()])],
+                1_000,
+            );
+            assert!(
+                matches!(resolve_ms_strict(&rumor), Err(StreamError::BadMs)),
+                "{malformed:?} must be malformed"
+            );
+        }
+
+        // Present but valueless is malformed, not an offset-0 default.
+        let valueless = build_rumor_secs(
+            9,
+            author.public_key(),
+            "x",
+            vec![Tag::custom(TAG_MS, Vec::<String>::new())],
+            1_000,
+        );
+        assert!(matches!(
+            resolve_ms_strict(&valueless),
+            Err(StreamError::BadMs)
+        ));
+
+        // A valued duplicate takes the first, matching Armada.
+        let repeated = build_rumor_secs(
+            9,
+            author.public_key(),
+            "x",
+            vec![
+                Tag::custom(TAG_MS, ["1".to_string()]),
+                Tag::custom(TAG_MS, ["2".to_string()]),
+            ],
+            1_000,
+        );
+        assert_eq!(resolve_ms_strict(&repeated).expect("resolves"), 1_000_001);
+    }
+}