Merge pull request 'feat(web): the world verbs on the wire (protocol 7, Phase 12a)' (#38) from feature/events-p12a-world-verbs into edge

Reviewed-on: #38

sidecar/src/main.rs

@@ -72,7 +72,26 @@ use tracing_subscriber::EnvFilter;
 /// index only the columns they already had, so the new fields ride inside the stored JSON and the
 /// new kind lands in `events` like any other. That is the dumb-forwarder property doing its job:
 /// the sidecar defines no schema for a frame's contents and so needs no change when they grow.
-pub const PROTOCOL_VERSION: u32 = 5;
+///
+/// v6 (Protocol 6): the first bump that is about a GUARANTEE rather than about data, and the first
+/// the sidecar mostly gets for free. Two things:
+///
+///   * **`idempotencyKey` on inbound commands.** A command that carries one is executed by the shard
+///     at most once; a repeat is answered with the original reply rather than re-run. That is what
+///     makes a world-writing verb retryable at all — until now a lost acknowledgement was
+///     indistinguishable from a command that never applied, so the website had to declare every
+///     write un-retryable and accept losing one rather than risk doubling it. The sidecar's part is
+///     to CARRY the key (it rides in the command body, which every write endpoint already passes
+///     through verbatim) and to understand the one new answer the shard can now give: `bridge.busy`,
+///     meaning a command under that key is still in flight. See `web::respond`.
+///   * **`champ.boss.killed` is a new kind**: a champion's defeat, with the damage table only the
+///     shard ever sees. It was previously inferable from `champ.update` going `bossUp` true then
+///     false alongside a nearby `mob.killed`, which is fragile and says nothing about who did the
+///     work. It lands in `events` and on the feed like any other kind, with no code here at all —
+///     the dumb-forwarder property again.
+///
+/// **No store migration.** Nothing gains a column; the new kind is persisted whole like every other.
+pub const PROTOCOL_VERSION: u32 = 7;
 
 // Not `#[tokio::main]`: on Windows the SCM dispatcher takes over this thread and starts the runtime
 // itself, on its own thread, once the service actually begins. The runtime is built by whichever

sidecar/src/web.rs

@@ -72,6 +72,31 @@ pub async fn serve(addr: &str, state: AppState) -> anyhow::Result<()> {
         .route("/admin/ban", post(admin_ban))
         .route("/admin/unban", post(admin_unban))
         .route("/admin/broadcast", post(admin_broadcast))
+        // The event plane (protocol 6, EVENTS_PLAN.md Phase 11b). Leases are a live config value
+        // the website holds for a bounded time; the shard restores baseline when the deadline
+        // passes whether or not anyone asks it to. GET lists the whole catalog with current values,
+        // which is the one read both `read()` and `inForce()` on the website's side are served by.
+        .route("/lease", get(lease_list).post(lease_apply))
+        .route("/lease/release", post(lease_release))
+        // The run-scoped participation ledger. `snapshot` is a POST despite being a read: it
+        // carries the caller's `idempotencyKey`, and on a well-attended run the shard walks its
+        // members across ticks rather than in one inbound call -- so a repeat arriving mid-walk is
+        // answered `bridge.busy`, and a read that can be refused as a repeat is not a GET.
+        .route("/participation", post(participation_open))
+        .route(
+            "/participation/:run_id/snapshot",
+            post(participation_snapshot),
+        )
+        .route("/participation/:run_id/close", post(participation_close))
+        // The world verbs (protocol 7, EVENTS_PLAN.md Phase 12a). Five things an event author
+        // can place -- creatures, an enhanced "boss", an oracle NPC, a temporary gate,
+        // decoration -- and ONE command family, because each of them ends in "an object exists
+        // and this run owns it". POST places, GET says what the run still owns, POST .../despawn
+        // gives it back. Ownership is held on the shard, so despawn cannot be pointed at a serial
+        // the run did not create.
+        .route("/world", post(world_spawn))
+        .route("/world/:run_id", get(world_owned))
+        .route("/world/:run_id/despawn", post(world_despawn))
         // Help-page (support) queue: snapshot the open queue, respond to / close a page.
         .route("/pages", get(pages_list))
         .route("/pages/:id/respond", post(page_respond))
@@ -246,13 +271,31 @@ fn constant_time_eq(a: &[u8], b: &[u8]) -> bool {
 
 // ---- shared reply handling ----
 
+/// Protocol 6. `bridge.busy` says a command carrying this `idempotencyKey` is already in flight on
+/// the shard: nothing was run, and the caller should come back.
+///
+/// It maps to **425 Too Early**, which is what that status is for — a server unwilling to risk
+/// processing a request that might be a replay. The obvious alternative, 409, is already the
+/// protocol-version gate's answer, and those two want opposite dispositions from a client: a version
+/// mismatch is a deployment fault nobody should retry, and a busy shard is a retry that should
+/// succeed on its own. Sharing a status would have made the difference readable only by inspecting
+/// the body, which is exactly how a retry loop ends up hiding a mismatched deployment.
+///
+/// It is checked BEFORE the `.error` suffix test in each responder below, and it is deliberately not
+/// spelled `bridge.busy.error`: nothing is wrong. The work is happening.
+const BUSY_KIND: &str = "bridge.busy";
+const BUSY_STATUS: StatusCode = StatusCode::TOO_EARLY;
+
 /// Turns an RPC result into an HTTP response. A `bridge.error` reply from the shard becomes a 4xx;
-/// a real reply is returned as-is; transport failures map to 503/504.
+/// a `bridge.busy` reply becomes a 425; a real reply is returned as-is; transport failures map to
+/// 503/504.
 fn respond(result: Result<Value, RpcError>) -> (StatusCode, Json<Value>) {
     match result {
         Ok(value) => {
             let kind = value.get("kind").and_then(|k| k.as_str()).unwrap_or("");
-            if kind == "bridge.error" || kind.ends_with(".error") {
+            if kind == BUSY_KIND {
+                (BUSY_STATUS, Json(value))
+            } else if kind == "bridge.error" || kind.ends_with(".error") {
                 let reason = value
                     .get("reason")
                     .and_then(|r| r.as_str())
@@ -286,7 +329,9 @@ fn respond_admin(result: Result<Value, RpcError>) -> (StatusCode, Json<Value>) {
     match result {
         Ok(value) => {
             let kind = value.get("kind").and_then(|k| k.as_str()).unwrap_or("");
-            if kind == "admin.error" {
+            if kind == BUSY_KIND {
+                (BUSY_STATUS, Json(value))
+            } else if kind == "admin.error" {
                 let reason = value
                     .get("reason")
                     .and_then(|r| r.as_str())
@@ -317,6 +362,56 @@ fn respond_admin(result: Result<Value, RpcError>) -> (StatusCode, Json<Value>) {
     }
 }
 
+/// Like `respond`, but for the event plane: leases and the participation ledger.
+///
+/// Two mappings are the point of it existing rather than reusing `respond`.
+///
+/// **`lease.drifted` is a 200.** The shard was asked to compare and set, it compared, and it
+/// refused to overwrite somebody's deliberate change -- that is the mechanism working, not a
+/// failure, and `cleanup.js` on the website treats `drifted` as a distinct successful outcome
+/// rather than an error. It is also why this is not a 409: 409 is the protocol-version gate's, and
+/// a version mismatch and a drifted lease want opposite dispositions from a caller. The same
+/// argument protocol 6 made for `bridge.busy` being a 425.
+///
+/// **The event plane being switched off is a 403**, not the 400 the generic responder's
+/// reason-sniffing would produce. `Bridge.EventsEnabled` is an operator's deliberate refusal to let
+/// the website change the world on a schedule, and telling the website it sent a bad request would
+/// send an administrator hunting a bug in a step that is written correctly.
+fn respond_event(result: Result<Value, RpcError>) -> (StatusCode, Json<Value>) {
+    match result {
+        Ok(value) => {
+            let kind = value.get("kind").and_then(|k| k.as_str()).unwrap_or("");
+            if kind == BUSY_KIND {
+                (BUSY_STATUS, Json(value))
+            } else if kind.ends_with(".error") {
+                let reason = value
+                    .get("reason")
+                    .and_then(|r| r.as_str())
+                    .unwrap_or("request rejected");
+                let code = if reason.contains("disabled") {
+                    StatusCode::FORBIDDEN
+                } else if reason.contains("no lease is offered") || reason.contains("not counting")
+                {
+                    StatusCode::NOT_FOUND
+                } else {
+                    StatusCode::BAD_REQUEST
+                };
+                (code, Json(value))
+            } else {
+                (StatusCode::OK, Json(value))
+            }
+        }
+        Err(RpcError::NoShard) => (
+            StatusCode::SERVICE_UNAVAILABLE,
+            Json(json!({"error": "shard not connected"})),
+        ),
+        Err(RpcError::Timeout) => (
+            StatusCode::GATEWAY_TIMEOUT,
+            Json(json!({"error": "shard did not reply in time"})),
+        ),
+    }
+}
+
 /// Like `respond`, but for the account-provisioning plane. Maps an `account.error` reply to a
 /// status by its reason: a name clash is a 409, the per-IP cap is a 429, a disabled/protected/
 /// refused action is a 403, an unknown target or "not linked" is a 404, anything else a 400.
@@ -324,7 +419,9 @@ fn respond_account(result: Result<Value, RpcError>) -> (StatusCode, Json<Value>)
     match result {
         Ok(value) => {
             let kind = value.get("kind").and_then(|k| k.as_str()).unwrap_or("");
-            if kind == "account.error" {
+            if kind == BUSY_KIND {
+                (BUSY_STATUS, Json(value))
+            } else if kind == "account.error" {
                 let reason = value
                     .get("reason")
                     .and_then(|r| r.as_str())
@@ -454,6 +551,16 @@ async fn link_delete(
 /// Forwards a staff moderation command to the shard, correlated on a fresh reqId. Injects `kind`
 /// and `reqId`, requiring the caller-supplied `actor` up front (the shard enforces it too). The
 /// body's remaining fields (account/serial/durationSec/reason/text/hue) pass straight through.
+///
+/// **Protocol 6: `idempotencyKey` is one of those remaining fields**, and passing it through is the
+/// whole of the sidecar's part in the guarantee. It is worth stating rather than leaving to the
+/// word "remaining", because a later refactor that narrowed this to a known field list would quietly
+/// turn every retried world write back into a possible duplicate, and nothing here would fail.
+///
+/// The key belongs to the CALLER's unit of work — the website's event step — so the sidecar neither
+/// generates one nor validates it. Note also that `reqId` is regenerated on every call: a retry
+/// carries the same idempotency key under a NEW correlation id, which is exactly why the shard
+/// re-stamps a replayed reply rather than echoing the id the first attempt used.
 async fn admin_call(st: &AppState, kind: &str, body: Value) -> (StatusCode, Json<Value>) {
     let mut obj = match body {
         Value::Object(m) => m,
@@ -504,6 +611,168 @@ async fn admin_broadcast(State(st): State<AppState>, Json(body): Json<Value>) ->
     admin_call(&st, "admin.broadcast", body).await
 }
 
+// ---- event plane handlers (protocol 6, Phase 11b) ----
+
+/// Forwards an event-plane command to the shard, correlated on a fresh reqId.
+///
+/// Deliberately NOT `admin_call`: that one requires an `actor`, because every verb behind it is a
+/// staff member pressing a button and the shard's audit trail has to name them. An event verb's
+/// author is a RUN, which the body already carries as `runId` -- and demanding an actor here would
+/// have the runner inventing a human name for something no human is doing.
+///
+/// Everything else about it is the same, and the `idempotencyKey` passthrough matters for the same
+/// reason it does there: the key is one of the body's remaining fields, and a refactor that
+/// narrowed this to a known field list would silently make every retried lease a possible duplicate.
+async fn event_call(st: &AppState, kind: &str, body: Value) -> (StatusCode, Json<Value>) {
+    let mut obj = match body {
+        Value::Object(m) => m,
+        Value::Null => serde_json::Map::new(),
+        _ => {
+            return (
+                StatusCode::BAD_REQUEST,
+                Json(json!({"error": "body must be a JSON object"})),
+            )
+        }
+    };
+
+    let req_id = st.rpc.next_req_id();
+    obj.insert("kind".to_string(), json!(kind));
+    obj.insert("reqId".to_string(), json!(req_id));
+
+    respond_event(st.rpc.call(&st.shard, Value::Object(obj), &req_id).await)
+}
+
+/// Every lease this shard offers, with what each is worth right now and what is holding it.
+///
+/// One read answers both questions the website asks about a lease: `read()` wants the current value
+/// before it applies anything, and `inForce()` wants to know whether the shard still has a record
+/// of the hold. Splitting them would be two round trips for one key.
+///
+/// **`held` means "the shard still has a record of this lease", not "the value is still
+/// overridden".** A lease whose deadline has already fired stays listed, with `expired: true`,
+/// until teardown collects its verdict -- otherwise a reconcile in that window would report it gone
+/// and the website would write off a correctly-working backstop as an orphaned resource.
+async fn lease_list(State(st): State<AppState>) -> impl IntoResponse {
+    event_call(&st, "lease.list", Value::Null).await
+}
+
+/// Body: {"key":"...","value":"...","holdMs":<ms>,"untilMs":<opt>,"runId":<opt>,"idempotencyKey":<opt>}.
+///
+/// **`holdMs` is authoritative and `untilMs` is carried for display.** An absolute deadline computed
+/// on the website and honoured on the shard is a deadline measured against two clocks, and a shard
+/// running ten minutes fast would restore a ten-minute lease the moment it took it. A duration is
+/// immune to that; the absolute time is still worth sending so a console can say when the hold ends.
+///
+/// Values cross as TEXT whatever the lease's declared type, because JSON would otherwise decide for
+/// us: `1200` and `1200.0` are one number to a parser and two strings to a compare-and-set.
+async fn lease_apply(State(st): State<AppState>, Json(body): Json<Value>) -> impl IntoResponse {
+    event_call(&st, "lease.apply", body).await
+}
+
+/// Body: {"key":"...","expected":"...","baseline":"...","idempotencyKey":<opt>}.
+///
+/// `expected` is what the event applied and `baseline` is what to put back, both out of the
+/// website's ledger rather than the shard's memory -- so a release still works after a reconnect,
+/// and a shard that has forgotten the lease entirely (a restart, which reverts every lease anyway)
+/// can answer honestly instead of refusing.
+///
+/// A mismatch comes back `lease.drifted` with a **200**: see `respond_event`.
+async fn lease_release(State(st): State<AppState>, Json(body): Json<Value>) -> impl IntoResponse {
+    event_call(&st, "lease.release", body).await
+}
+
+/// Body: {"runId":"...","map":"Felucca","x":N,"y":N,"radius":N,"holdMs":<opt>}.
+///
+/// Declares where a run happens and starts counting who is there. The area is a map, a point and a
+/// radius rather than a region name, because protocol 6's own live walk established that the most
+/// specific region containing an event is routinely anonymous.
+async fn participation_open(
+    State(st): State<AppState>,
+    Json(body): Json<Value>,
+) -> impl IntoResponse {
+    event_call(&st, "participation.open", body).await
+}
+
+/// Body: {"idempotencyKey":<opt>}. Answers the run's tally, best-effort resolved to accounts.
+///
+/// A POST for a read, and the reason is worth keeping: on a well-attended run the shard walks its
+/// members in chunks across Core ticks rather than handing the whole resolve to one inbound call,
+/// so the handler completes after its call returned and a repeat arriving in between is answered
+/// `bridge.busy`. A read that can legitimately be refused as a repeat in flight is not a GET.
+async fn participation_snapshot(
+    State(st): State<AppState>,
+    Path(run_id): Path<String>,
+    Json(body): Json<Value>,
+) -> impl IntoResponse {
+    let mut obj = match body {
+        Value::Object(m) => m,
+        _ => serde_json::Map::new(),
+    };
+    obj.insert("runId".to_string(), json!(run_id));
+    event_call(&st, "participation.snapshot", Value::Object(obj)).await
+}
+
+/// Body: {"idempotencyKey":<opt>}. Stops counting; the tally stays readable through the shard's
+/// grace window, because closing an event and collecting its results are two steps and either can
+/// be retried.
+async fn participation_close(
+    State(st): State<AppState>,
+    Path(run_id): Path<String>,
+    Json(body): Json<Value>,
+) -> impl IntoResponse {
+    let mut obj = match body {
+        Value::Object(m) => m,
+        _ => serde_json::Map::new(),
+    };
+    obj.insert("runId".to_string(), json!(run_id));
+    event_call(&st, "participation.close", Value::Object(obj)).await
+}
+
+/// Body: {"runId":"...","what":"creature|boss|npc|gate|decor","map":"...","x":N,"y":N,...}.
+///
+/// One route for five author-facing verbs. The `what` discriminator is a wire detail: the
+/// differences between them -- a boss's multipliers, an oracle's lines, a gate's destination and
+/// `holdMs` -- are fields on one command rather than five commands, so there is one ledger shape,
+/// one teardown path and one reconcile instead of five near-identical ones in three repos.
+///
+/// The shard registers every serial it places against the run and PERSISTS that registry beside
+/// the world save, which is what makes `world_despawn` below safe: a spawned creature survives a
+/// restart, so an in-memory registry would leave the website holding serials the shard would not
+/// vouch for.
+async fn world_spawn(State(st): State<AppState>, Json(body): Json<Value>) -> impl IntoResponse {
+    event_call(&st, "world.spawn", body).await
+}
+
+/// What the run still owns, and the answer the website's `reconcile()` is built on.
+///
+/// A GET, unlike `participation_snapshot`: it carries no idempotency key and the shard answers it
+/// in one pass, pruning rows whose object the world has already lost as it walks. Anything not
+/// listed is gone -- which is the shape core wants, because it takes a row out of its ledger only
+/// on an explicit reply and this is that reply.
+async fn world_owned(State(st): State<AppState>, Path(run_id): Path<String>) -> impl IntoResponse {
+    event_call(&st, "world.owned", json!({ "runId": run_id })).await
+}
+
+/// Body: {"serials":[...]} -- or no serials at all, which means everything the run owns and is the
+/// call teardown actually makes.
+///
+/// Three answers, and the split is why the shard keeps a registry at all. `removed` was found and
+/// deleted; `gone` was owned but already absent, which is what happens when a player kills an event
+/// creature and is a SUCCESS; `refused` was never this run's to delete, and is the only answer here
+/// that means somebody asked for something they should not have.
+async fn world_despawn(
+    State(st): State<AppState>,
+    Path(run_id): Path<String>,
+    Json(body): Json<Value>,
+) -> impl IntoResponse {
+    let mut obj = match body {
+        Value::Object(m) => m,
+        _ => serde_json::Map::new(),
+    };
+    obj.insert("runId".to_string(), json!(run_id));
+    event_call(&st, "world.despawn", Value::Object(obj)).await
+}
+
 // ---- help-page queue handlers ----
 
 /// The open help-page queue, correlated on reqId. Returns a pages.list.
@@ -978,3 +1247,210 @@ async fn ws_client(mut socket: WebSocket, state: AppState) {
 
     info!("ws client disconnected");
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn reply(kind: &str) -> Result<Value, RpcError> {
+        Ok(json!({"t": 1, "kind": kind, "reqId": "r-9"}))
+    }
+
+    /// Protocol 6. Every responder must recognise `bridge.busy`, because every write plane can be
+    /// retried: the staff plane, the account plane and the plain command plane all reach handlers
+    /// that a keyed retry can arrive at. A responder that missed it would return 200 with a body
+    /// saying nothing happened, which is the worst of the three possible answers.
+    #[test]
+    fn busy_maps_to_425_on_every_plane() {
+        assert_eq!(respond(reply("bridge.busy")).0, StatusCode::TOO_EARLY);
+        assert_eq!(respond_admin(reply("bridge.busy")).0, StatusCode::TOO_EARLY);
+        assert_eq!(
+            respond_account(reply("bridge.busy")).0,
+            StatusCode::TOO_EARLY
+        );
+        assert_eq!(respond_event(reply("bridge.busy")).0, StatusCode::TOO_EARLY);
+    }
+
+    /// The event plane is the FIRST place `bridge.busy` is reachable on a live shard rather than
+    /// only in a unit test: `participation.snapshot` walks a well-attended run's members across
+    /// Core ticks, so it completes after its inbound call returned and a repeat can genuinely land
+    /// mid-flight. 11a built the door and had nothing to walk through it.
+    #[test]
+    fn a_drifted_lease_is_a_200_not_a_409() {
+        let value =
+            json!({"kind": "lease.drifted", "key": "PlayerCaps.SkillCap", "current": "1300"});
+        let (status, body) = respond_event(Ok(value));
+
+        // The shard was asked to compare and set, it compared, and it declined to overwrite
+        // somebody's deliberate change. That is the mechanism working; the website records
+        // `drifted` as a distinct successful outcome rather than an error.
+        assert_eq!(status, StatusCode::OK);
+        assert_eq!(body.0.get("current").and_then(|v| v.as_str()), Some("1300"));
+
+        // And explicitly not the version gate's status, for the reason 425 is not either: a
+        // mismatched deployment and a moved value want opposite dispositions from a caller.
+        assert_ne!(status, StatusCode::CONFLICT);
+    }
+
+    /// The event plane being switched off is an operator's refusal, not a malformed request. A 400
+    /// would send an administrator hunting a bug in a step that is written correctly.
+    #[test]
+    fn the_event_gate_being_off_is_a_403() {
+        assert_eq!(
+            respond_event(Ok(json!({
+                "kind": "lease.error",
+                "reason": "the event plane is disabled on this shard (Bridge.EventsEnabled)"
+            })))
+            .0,
+            StatusCode::FORBIDDEN
+        );
+        assert_eq!(
+            respond_event(Ok(json!({
+                "kind": "participation.error",
+                "reason": "the event plane is disabled on this shard (Bridge.EventsEnabled)"
+            })))
+            .0,
+            StatusCode::FORBIDDEN
+        );
+    }
+
+    /// Protocol 7's world verbs go through the same responder, and this pins the two mappings
+    /// they depend on rather than trusting that the reason-sniffing above keeps covering a kind
+    /// it was written before.
+    ///
+    /// A CEILING refusal is a 400 on purpose. It is permanent -- retrying "you asked for 80
+    /// creatures and this shard places 30" gets the same answer forever -- and it is the module's
+    /// `PERMANENT_STATUSES` that has to see it as such, so classifying it as anything retryable
+    /// would put a run in a loop against a limit that will never move.
+    #[test]
+    fn a_world_refusal_is_a_400_and_the_gate_is_still_a_403() {
+        assert_eq!(
+            respond_event(Ok(json!({
+                "kind": "world.error",
+                "action": "spawn",
+                "reason": "this shard places 1 to 30 of 'creature' at a time, and 80 was asked for"
+            })))
+            .0,
+            StatusCode::BAD_REQUEST
+        );
+        assert_eq!(
+            respond_event(Ok(json!({
+                "kind": "world.error",
+                "action": "spawn",
+                "reason": "the event plane is disabled on this shard (Bridge.EventsEnabled)"
+            })))
+            .0,
+            StatusCode::FORBIDDEN
+        );
+    }
+
+    /// A run the shard has no registry rows for answers with an EMPTY hand, not a 404, and the
+    /// distinction is load-bearing for reconcile.
+    ///
+    /// "This run owns nothing" and "I have never heard of this run" are the same fact once the
+    /// registry is the only record of ownership, and they stay the same fact across a restart:
+    /// the registry is written by `EventSink.WorldSave`, so it and the objects it describes are
+    /// saved and lost together. A 404 here would make the website treat a run that legitimately
+    /// owns nothing as a shard it could not reach.
+    #[test]
+    fn a_run_owning_nothing_is_an_empty_list_not_a_404() {
+        let (status, body) = respond_event(Ok(json!({
+            "kind": "world.owned.ok",
+            "runId": "77",
+            "owned": [],
+            "pruned": 0
+        })));
+
+        assert_eq!(status, StatusCode::OK);
+        assert_eq!(
+            body.0
+                .get("owned")
+                .and_then(|v| v.as_array())
+                .map(|a| a.len()),
+            Some(0)
+        );
+    }
+
+    /// An unknown lease key and an unknown run are not-founds; anything else the shard refuses is a
+    /// bad request. The catalog is short and a typo in a step is the likely cause of both.
+    #[test]
+    fn unknown_lease_and_run_are_404s() {
+        assert_eq!(
+            respond_event(Ok(json!({
+                "kind": "lease.error",
+                "reason": "no lease is offered for key 'Loot.MaxProps'"
+            })))
+            .0,
+            StatusCode::NOT_FOUND
+        );
+        assert_eq!(
+            respond_event(Ok(json!({
+                "kind": "participation.error",
+                "reason": "this shard is not counting run '42'"
+            })))
+            .0,
+            StatusCode::NOT_FOUND
+        );
+        assert_eq!(
+            respond_event(Ok(json!({
+                "kind": "lease.error",
+                "reason": "a lease needs a positive holdMs"
+            })))
+            .0,
+            StatusCode::BAD_REQUEST
+        );
+    }
+
+    /// A lease taken, a tally answered: an ordinary success carries straight through.
+    #[test]
+    fn event_successes_are_200s() {
+        assert_eq!(respond_event(reply("lease.ok")).0, StatusCode::OK);
+        assert_eq!(respond_event(reply("lease.list.ok")).0, StatusCode::OK);
+        assert_eq!(respond_event(reply("participation.ok")).0, StatusCode::OK);
+        assert_eq!(
+            respond_event(reply("participation.snapshot.ok")).0,
+            StatusCode::OK
+        );
+    }
+
+    /// 425 must not collide with the protocol-version gate's 409: a mismatch is a deployment fault
+    /// nobody should retry, a busy shard is a retry that will succeed. Same-status would make the
+    /// two readable only by inspecting the body.
+    #[test]
+    fn busy_is_not_the_version_gates_status() {
+        assert_ne!(BUSY_STATUS, StatusCode::CONFLICT);
+    }
+
+    /// A replayed reply is an ordinary success. The shard marks it `replayed: true` for the log, and
+    /// the caller must be able to treat it exactly as it would have treated the answer it lost.
+    #[test]
+    fn a_replayed_reply_is_still_a_200() {
+        let value = json!({"t": 1, "kind": "admin.ok", "reqId": "r-9", "replayed": true});
+        let (status, body) = respond_admin(Ok(value));
+        assert_eq!(status, StatusCode::OK);
+        assert_eq!(body.0.get("replayed").and_then(|v| v.as_bool()), Some(true));
+    }
+
+    /// The error mapping the busy arm is threaded in front of must be untouched by it.
+    #[test]
+    fn errors_still_map_as_before() {
+        assert_eq!(
+            respond(Ok(
+                json!({"kind": "bridge.error", "reason": "unknown account"})
+            ))
+            .0,
+            StatusCode::NOT_FOUND
+        );
+        assert_eq!(
+            respond_admin(Ok(json!({"kind": "admin.error", "reason": "protected"}))).0,
+            StatusCode::FORBIDDEN
+        );
+        assert_eq!(
+            respond_account(Ok(
+                json!({"kind": "account.error", "reason": "already exists"})
+            ))
+            .0,
+            StatusCode::CONFLICT
+        );
+    }
+}