agent icon: 404 when unconfigured, client-side fallback

hive_sh4re::assets::branding_svg() resolved a server-side default
icon at runtime from HIVE_ASSETS_DIR — the only consumer was
serve_icon(), which fell back to it whenever the agent had no
`hyperhive.icon` override. Removed both the fallback and the
function: serve_icon() now 404s when /etc/hyperhive/icon.svg is
absent, and the per-agent web UI (app.js) picks up the existing
dashboard swarm.js pattern — swap the <img> src to the
frontend-bundled /favicon.svg on load failure, guarded against
looping if the fallback itself 404s.

Updated the doc/comment claims that said the server always returns
an image (docs/web-ui/agent.md, nix/agent-modules/default.nix, the
hive-c0re/forge/users.rs comment referencing the old shared-asset
set). forge-avatar-sync and the matrix avatar sync are unaffected —
both are gated on hyperhive.icon != null and never depended on the
removed fallback.

docs/web-ui/agent.md

@@ -383,10 +383,10 @@ shaped).
   earliest recorded turn with an adaptive bucket width.
 - `GET /icon` — agent's icon as `image/svg+xml`. Returns
   `/etc/hyperhive/icon.svg` (set via `hyperhive.icon` in `agent.nix`)
-  when present, otherwise the bundled default hyperhive logo. Always
-  returns an image — consumers (dashboard container row, per-agent
-  favicon) can hit `/icon` unconditionally without probing for a
-  custom config.
+  when present, otherwise **404** — there is no server-side default.
+  Consumers (dashboard container row, this page's own header icon)
+  hit `/icon` optimistically and fall back client-side on load failure
+  to the frontend-bundled `/favicon.svg` rather than probing first.
 - `GET /events/history` — replay buffer for the terminal.
 - `GET /screen` — VNC viewer page (minimal RFB-over-WebSocket
   renderer — deliberately thin, just enough to display the

frontend/packages/agent/src/app.js

@@ -38,6 +38,22 @@ window.marked = marked;
   // native confirm()/alert() dialogs that broke out of the page theme.
   bindAsyncForms(() => refreshState());
 
+  // ─── header icon fallback ───────────────────────────────────────────────
+  // `/icon` 404s when this agent has no `hyperhive.icon` override (see
+  // hive-agent::web_ui::screen::serve_icon — no bundled server-side
+  // default any more). Mirrors the dashboard's `swarm.js` `/favicon.svg`
+  // fallback: fire-and-forget load, swap on failure, guarded so a 404 on
+  // the fallback itself can't loop.
+  (function bindHeaderIconFallback() {
+    const iconImg = document.querySelector('.agent-icon');
+    if (!iconImg) return;
+    iconImg.addEventListener('error', () => {
+      if (iconImg.dataset.fallback) return;
+      iconImg.dataset.fallback = '1';
+      iconImg.src = '/favicon.svg';
+    });
+  })();
+
   // ─── side panel (singleton drawer for inbox + loose-ends flyouts) ──────
   // The shared `<hive-side-panel>` element (see @hive/shared/side-panel.js
   // for the chrome/behavior it owns), created once, eagerly, when this

hive-agent/src/web_ui/screen.rs

@@ -11,20 +11,18 @@ use super::AppState;
 
 /// This agent's icon. Serves the operator-configured SVG from
 /// `/etc/hyperhive/icon.svg` (set via the `hyperhive.icon` agent.nix
-/// option) when present, otherwise the bundled default hyperhive logo.
-/// Always returns an image, so consumers (dashboard, favicon) can hit
-/// `/icon` unconditionally without probing whether one is configured.
-pub(super) async fn serve_icon() -> impl IntoResponse {
-    // Per-agent icon overrides go through `/etc/hyperhive/icon.svg`
-    // (set via the `hyperhive.icon` agent.nix option); the bundled
-    // default is resolved at runtime from
-    // `$HIVE_ASSETS_DIR/branding/hyperhive.svg`. If neither file can
-    // be read we serve an empty body — keeps the response a valid SVG
-    // content-type without a panic on a misconfigured container.
-    let body = std::fs::read_to_string("/etc/hyperhive/icon.svg").unwrap_or_else(|_| {
-        std::fs::read_to_string(hive_sh4re::assets::branding_svg()).unwrap_or_default()
-    });
-    ([("content-type", "image/svg+xml")], body)
+/// option) when present, otherwise **404** — there is no bundled
+/// server-side default any more (that was `hive_sh4re::assets::
+/// branding_svg`, now removed). Consumers fall back client-side: the
+/// dashboard's `swarm.js` and this agent's own `app.js` both swap an
+/// `/icon` load failure to the frontend-bundled `/favicon.svg` rather
+/// than probing first, so a 404 here is the expected "unconfigured"
+/// signal, not an error case to work around.
+pub(super) async fn serve_icon() -> Response {
+    match std::fs::read_to_string("/etc/hyperhive/icon.svg") {
+        Ok(body) => ([("content-type", "image/svg+xml")], body).into_response(),
+        Err(_) => (StatusCode::NOT_FOUND, "no icon configured").into_response(),
+    }
 }
 
 /// WebSocket handler: upgrade then pump bytes between the WS client and

hive-c0re/src/forge/users.rs

@@ -27,7 +27,9 @@ use crate::paths::FORGE_CORE_TOKEN as CORE_TOKEN_PATH;
 // Avatar PNG paths are resolved by `core_avatar_png_path` /
 // `config_org_avatar_png_path` below — only-used-here, so they live
 // in this module rather than the shared `hive_sh4re::assets` helpers
-// (which stay for paths every crate needs, e.g. `branding_svg`).
+// (which now hold only `prompt_template`, the one asset path every
+// crate needs — the agent icon, the last other one, moved off the
+// shared-asset model entirely; see `hive-agent::web_ui::screen`).
 
 /// `$HIVE_ASSETS_DIR/branding/hyperhive.png` — the core mark,
 /// rasterised. Not independently configurable (unlike the org avatar

hive-sh4re/src/assets.rs

@@ -16,10 +16,13 @@
 //! layout.
 //!
 //! Each crate that wants a specific asset goes through one of the
-//! typed helpers (`branding_svg()`, `prompt_template()`, …) so the
-//! lookup contract is centralised. Missing files panic at first
-//! call with a clear "set `HIVE_ASSETS_DIR` + put the file at …"
-//! message.
+//! typed helpers (currently just `prompt_template()` — the branding
+//! SVG used to live here too; the per-agent icon now 404s server-side
+//! when unconfigured and falls back to a frontend-bundled default
+//! client-side instead of a server-resolved runtime path, see
+//! `hive-agent::web_ui::screen::serve_icon`) so the lookup contract is
+//! centralised. Missing files panic at first call with a clear "set
+//! `HIVE_ASSETS_DIR` + put the file at …" message.
 
 use std::path::PathBuf;
 
@@ -41,15 +44,6 @@ fn dir() -> PathBuf {
     }
 }
 
-/// `$HIVE_ASSETS_DIR/branding/hyperhive.svg` — the project's primary
-/// mark. Loaded by the per-agent web UI as its default icon
-/// (`/agents/<n>/icon.svg` falls through here when the agent didn't
-/// override `hyperhive.icon` in its `agent.nix`).
-#[must_use]
-pub fn branding_svg() -> PathBuf {
-    dir().join("branding/hyperhive.svg")
-}
-
 /// `$HIVE_ASSETS_DIR/prompts/system.md` — the claude system prompt
 /// template. `hive-agent::prompt::render` filters the role markers
 /// inside it per agent / manager flavor.

nix/agent-modules/default.nix

@@ -55,9 +55,10 @@
       the SVG into the agent's config repo next to `agent.nix` and
       reference it as a relative path (`./icon.svg`).
 
-      When null (the default) the agent falls back to the shared
-      hyperhive logo. The harness serves the icon (configured or
-      default) at `GET /icon` on the per-agent web port.
+      When null (the default), `GET /icon` on the per-agent web port
+      404s and consumers (dashboard, this agent's own page header)
+      fall back client-side to the frontend-bundled `/favicon.svg`
+      rather than a server-resolved default.
     '';
   };
 
@@ -113,9 +114,9 @@
 
     # Operator-set per-agent icon (hyperhive.icon). When configured, the
     # SVG lands at /etc/hyperhive/icon.svg; the harness serves it at
-    # GET /icon, falling back to the bundled hyperhive logo when absent.
-    # Consumed by forge-avatar-sync (./forge.nix) and the matrix avatar
-    # sync (./matrix.nix) too.
+    # GET /icon, 404ing when absent (client-side fallback, no
+    # server-side default). Consumed by forge-avatar-sync (./forge.nix)
+    # and the matrix avatar sync (./matrix.nix) too.
     environment.etc."hyperhive/icon.svg" = lib.mkIf (config.hyperhive.icon != null) {
       source = config.hyperhive.icon;
     };