fix: rediscover hive Space by hardcoded name, not a room alias

Per mara's review: drop the #hive:<server> room alias (special chars) and
rediscover the canonical Space by its hardcoded plain name instead.

ensure_hive_space dedup is now:
  1. room-id file present -> reuse it
  2. else scan the admin's joined rooms for the m.space named HIVE_SPACE_NAME
     ('hive') and adopt the first match (re-persisting the file) -> recovers
     the existing space after a state wipe instead of creating a duplicate
  3. else createRoom (plain name, no alias)

find_space_by_name walks /joined_rooms and checks each room's m.room.create
type == m.space and m.room.name == 'hive'. No alias, no special-char anchor.
server_name is no longer needed by ensure_hive_space (dropped the param).

hive-c0re/src/matrix.rs

@@ -45,6 +45,12 @@ const PASSWORD_BYTES: usize = 32;
 /// first registered user automatically. Not an agent; has no state dir.
 pub const HIVE_ADMIN_LOCALPART: &str = "hive";
 
+/// Display name of the hive Space. Plain text, no special characters, so
+/// the Space stays rediscoverable by name (no room alias needed) even when
+/// the persisted room-id file is lost — preventing duplicate spaces from
+/// being created on the next sweep.
+pub const HIVE_SPACE_NAME: &str = "hive";
+
 /// Host path for the hive admin matrix access token. Outside every
 /// purgeable path — not deleted by `destroy --purge` on any agent.
 #[must_use]
@@ -945,30 +951,119 @@ pub fn read_admin_token() -> Result<String> {
         })
 }
 
-/// Create the hive Matrix Space room using the admin account and persist
-/// its room ID to [`hive_space_room_id_path()`]. Idempotent — returns
-/// the stored room ID immediately if the file already exists.
+/// Persist the hive Space room id to [`hive_space_room_id_path()`] (0600).
+fn persist_space_room_id(room_id: &str) -> Result<()> {
+    use std::os::unix::fs::PermissionsExt;
+    let path = hive_space_room_id_path();
+    if let Some(parent) = path.parent() {
+        std::fs::create_dir_all(parent).ok();
+    }
+    std::fs::write(&path, format!("{room_id}\n"))
+        .with_context(|| format!("matrix: write space room_id to {}", path.display()))?;
+    let _ = std::fs::set_permissions(&path, std::fs::Permissions::from_mode(0o600));
+    Ok(())
+}
+
+/// Scan the admin account's joined rooms for the canonical hive Space: the
+/// `m.space` whose name is [`HIVE_SPACE_NAME`]. Returns the first match
+/// (deterministic per the homeserver's joined-rooms order) so a lost
+/// room-id file recovers the existing space instead of spawning a
+/// duplicate. `None` if the homeserver is unreachable or no match exists.
 ///
-/// The Space is a private `m.space` room owned by `@hive`. All agents
-/// are invited after their accounts are provisioned in [`ensure_all`].
+/// Name-based (not alias-based) rediscovery keeps the Space free of any
+/// special-char room alias — the hardcoded plain name is the anchor.
+async fn find_space_by_name(client: &reqwest::Client, admin_token: &str) -> Option<String> {
+    let joined_url = format!("{MATRIX_HTTP}/_matrix/client/v3/joined_rooms");
+    let joined: serde_json::Value = client
+        .get(&joined_url)
+        .bearer_auth(admin_token)
+        .send()
+        .await
+        .ok()?
+        .json()
+        .await
+        .ok()?;
+    let rooms = joined["joined_rooms"].as_array()?;
+    for room in rooms {
+        let Some(room_id) = room.as_str() else {
+            continue;
+        };
+        let encoded = encode_room_id_for_url(room_id);
+        // Must be an m.space (m.room.create `type`).
+        let create_url =
+            format!("{MATRIX_HTTP}/_matrix/client/v3/rooms/{encoded}/state/m.room.create/");
+        let is_space = match client
+            .get(&create_url)
+            .bearer_auth(admin_token)
+            .send()
+            .await
+        {
+            Ok(r) if r.status().is_success() => r
+                .json::<serde_json::Value>()
+                .await
+                .ok()
+                .is_some_and(|c| c["type"].as_str() == Some("m.space")),
+            _ => false,
+        };
+        if !is_space {
+            continue;
+        }
+        // …and named HIVE_SPACE_NAME (m.room.name `name`).
+        let name_url =
+            format!("{MATRIX_HTTP}/_matrix/client/v3/rooms/{encoded}/state/m.room.name/");
+        let name_matches = match client.get(&name_url).bearer_auth(admin_token).send().await {
+            Ok(r) if r.status().is_success() => r
+                .json::<serde_json::Value>()
+                .await
+                .ok()
+                .is_some_and(|n| n["name"].as_str() == Some(HIVE_SPACE_NAME)),
+            _ => false,
+        };
+        if name_matches {
+            return Some(room_id.to_owned());
+        }
+    }
+    None
+}
+
+/// Create (or recover) the hive Matrix Space and persist its room ID to
+/// [`hive_space_room_id_path()`]. The Space is a private `m.space` owned by
+/// `@hive`, identified by its hardcoded name [`HIVE_SPACE_NAME`] (no alias).
+///
+/// Dedup strategy (single canonical space):
+///  1. If the room-id file exists, reuse it.
+///  2. Otherwise, rediscover by scanning the admin's joined rooms for the
+///     `m.space` named [`HIVE_SPACE_NAME`] and adopt it (re-persisting the
+///     file). This recovers the existing space after a state wipe instead
+///     of creating a duplicate.
+///  3. Only if neither yields a room do we `createRoom`.
 ///
 /// # Errors
 ///
-/// Returns an error if the Matrix homeserver is unreachable, the
-/// `createRoom` call fails, or the room-ID file cannot be written.
+/// Returns an error if the homeserver is unreachable, `createRoom` fails,
+/// or the room-ID file cannot be written.
 pub async fn ensure_hive_space(client: &reqwest::Client, admin_token: &str) -> Result<String> {
-    use std::os::unix::fs::PermissionsExt;
-    let path = hive_space_room_id_path();
-    if let Ok(existing) = std::fs::read_to_string(&path) {
+    // 1. Stored room id wins (fast path).
+    if let Ok(existing) = std::fs::read_to_string(hive_space_room_id_path()) {
         let trimmed = existing.trim().to_owned();
         if !trimmed.is_empty() {
             tracing::debug!(room_id = %trimmed, "matrix: hive space already provisioned");
             return Ok(trimmed);
         }
     }
+
+    // 2. No stored id — rediscover the existing space by its hardcoded name
+    //    before creating a new one (prevents duplicate spaces after a wipe).
+    if let Some(room_id) = find_space_by_name(client, admin_token).await {
+        persist_space_room_id(&room_id)?;
+        tracing::info!(%room_id, "matrix: recovered hive space by name");
+        return Ok(room_id);
+    }
+
+    // 3. Create the space (plain hardcoded name, no alias).
     let url = format!("{MATRIX_HTTP}/_matrix/client/v3/createRoom");
     let body = serde_json::json!({
-        "name": "hive",
+        "name": HIVE_SPACE_NAME,
         "creation_content": { "type": "m.space" },
         "preset": "private_chat",
         "visibility": "private",
@@ -992,12 +1087,7 @@ pub async fn ensure_hive_space(client: &reqwest::Client, admin_token: &str) -> R
         .as_str()
         .with_context(|| format!("matrix: createRoom missing room_id: {json}"))?
         .to_owned();
-    if let Some(parent) = path.parent() {
-        std::fs::create_dir_all(parent).ok();
-    }
-    std::fs::write(&path, format!("{room_id}\n"))
-        .with_context(|| format!("matrix: write space room_id to {}", path.display()))?;
-    let _ = std::fs::set_permissions(&path, std::fs::Permissions::from_mode(0o600));
+    persist_space_room_id(&room_id)?;
     tracing::info!(%room_id, "matrix: created hive space");
     Ok(room_id)
 }
@@ -1100,6 +1190,14 @@ pub async fn ensure_all() {
             return;
         }
     };
+    // server_name first — the agent invites need it (fully-qualified user ids).
+    let server_name = match discover_server_name(&client).await {
+        Ok(s) => s,
+        Err(e) => {
+            tracing::warn!(error = ?e, "matrix: discover_server_name failed; skipping space provisioning");
+            return;
+        }
+    };
     let room_id = match ensure_hive_space(&client, &admin_token).await {
         Ok(id) => id,
         Err(e) => {
@@ -1107,13 +1205,6 @@ pub async fn ensure_all() {
             return;
         }
     };
-    let server_name = match discover_server_name(&client).await {
-        Ok(s) => s,
-        Err(e) => {
-            tracing::warn!(error = ?e, "matrix: discover_server_name failed; skipping space invites");
-            return;
-        }
-    };
     // Invite @hive admin first, then all agents.
     if let Err(e) = invite_to_room(
         &client,