fix(viewer): surface health status from non-2xx /agentmemory/health responses (#1046)

* fix(viewer): surface health status from non-2xx /agentmemory/health responses

The health endpoint intentionally returns HTTP 503 when status is
"critical" (src/triggers/api.ts), with a valid JSON body describing
the degraded state. The viewer's shared api() fetch helper treated
any non-ok response as a hard failure and discarded the body,
returning null - so renderDashboard's `h.status || 'unknown'` fallback
always showed "unknown" for a critical backend instead of "critical".

Parse and return the JSON body on non-ok responses too (falling back
to null only if the body isn't valid JSON), so the dashboard reflects
the real health status regardless of the HTTP status code used to
carry it.

Fixes #1019

Signed-off-by: Vidit Gujrathi <223816573+viditchess64@users.noreply.github.com>

* fix(viewer): log non-2xx JSON parse failures at debug level

Address CodeRabbit review: don't silently swallow the parse error when
a non-2xx response body isn't valid JSON - log it at debug level to
help diagnose unexpected content types.

Signed-off-by: Vidit Gujrathi <223816573+viditchess64@users.noreply.github.com>

* fix(viewer): restore non-2xx -> null contract in api(), special-case health

Per review: changing the shared api() helper to return parsed bodies on
non-2xx responses broke callers that treat null as "request failed"
(e.g. loadGraph's disabled/error state). Restore the null contract as
the default and let only the health call opt in via readErrorBody,
since /agentmemory/health intentionally responds 503 with a valid JSON
body when status is critical (#1019).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Signed-off-by: Vidit Gujrathi <223816573+viditchess64@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: viditchess64

src/viewer/index.html

@@ -1244,11 +1244,24 @@ <h1>agentmemory</h1>
           headers.Authorization = 'Bearer ' + viewerToken;
         }
         var fetchOpts = Object.assign({}, opts || {}, { headers: headers });
+        var readErrorBody = fetchOpts.readErrorBody;
+        delete fetchOpts.readErrorBody;
         var res = await fetch(url, fetchOpts);
         if (!res.ok) {
           if (res.status === 401) showViewerAuthPrompt();
           console.warn('[viewer] API ' + (fetchOpts.method || 'GET') + ' ' + path + ' returned ' + res.status);
-          return null;
+          // Non-2xx responses resolve to null so callers can keep treating
+          // null as "request failed" (e.g. loadGraph's disabled/error state).
+          // The health endpoint opts out via readErrorBody: it intentionally
+          // responds 503 with a valid JSON body when status is "critical"
+          // (see #1019), and the dashboard badge needs that body.
+          if (!readErrorBody) return null;
+          try {
+            return await res.json();
+          } catch (parseErr) {
+            console.debug('[viewer] API ' + path + ' non-2xx body was not JSON:', parseErr);
+            return null;
+          }
         }
         hideViewerAuthPrompt();
         return await res.json();
@@ -1344,7 +1357,7 @@ <h1>agentmemory</h1>
       el.innerHTML = '<div class="loading">Loading dashboard...</div>';
       try {
         var results = await Promise.all([
-          apiGet('health'),
+          api('health', { readErrorBody: true }),
           apiGet('sessions'),
           apiGet('memories?latest=true&limit=500'),
           apiGet('graph/stats'),