dashboard: build-log side-panel viewer in agent card (#726 phase 3)

Adds a `↳ build logs · {agent}` drill-in to every agent card that
opens the side panel and fetches the last 10 build-log headers from
GET /api/build-logs/{agent}. Each row shows a status chip (ok/fail/
running), kind, age, and truncated cmdline. Clicking a row lazily
fetches the full stdout+stderr from GET /api/build-logs/id/{id} and
expands it inline as a scrollable pre.

CSS additions: .build-logs-{panel,toolbar,list,item,row-btn,...} plus
.badge-ok/.badge-fail/.badge-running status chips shared with future
uses. docs/web-ui.md updated with the new drill-in and the new badge
classes.

docs/web-ui/dashboard.md

@@ -369,6 +369,15 @@ fetch entirely.
     layout so the `<pre>` log surface fills the full remaining panel
     height; scroll happens inside the `<pre>`, not the side
     panel body.
+  - `↳ build logs · <agent>` — opens the side panel and fetches
+    the last 10 build-log headers via
+    `GET /api/build-logs/{agent}` (status chip + kind + age +
+    truncated cmdline per row). Clicking a row lazy-fetches its
+    full stdout+stderr from `GET /api/build-logs/id/{id}` and
+    expands it inline as a scrollable `<pre>`. A refresh button
+    re-fetches the header list. Backed by the `build_logs.sqlite`
+    store that `lifecycle::run` and `lifecycle::prebuild_toplevel`
+    write into.
   - Plain navigation links (config repo, forge profile,
     `dashboardLinks` extras) now live in the icon-only nav strip
     on Line 1 — see above. The agent's `config` link

frontend/packages/dashboard/src/dashboard.css

@@ -504,6 +504,90 @@ a:hover {
   word-break: normal;
 }
 
+/* Build-log side-panel viewer. Same general shape as the journald
+   viewer: a toolbar above a scrollable list of log header rows;
+   clicking a row expands full stdout+stderr inline. */
+.build-logs-panel {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+  gap: 0.4em;
+}
+.build-logs-toolbar {
+  flex: 0 0 auto;
+  display: flex;
+  gap: 0.5em;
+  align-items: center;
+}
+.build-logs-refresh { font-size: 0.75em; padding: 0.15em 0.5em; }
+.build-logs-list {
+  list-style: none;
+  margin: 0;
+  padding: 0;
+  flex: 1 1 0;
+  min-height: 0;
+  overflow-y: auto;
+  display: flex;
+  flex-direction: column;
+  gap: 0.25em;
+}
+.build-logs-loading,
+.build-logs-empty,
+.build-logs-error {
+  padding: 0.4em 0.6em;
+  font-size: 0.85em;
+  color: var(--subtext0);
+}
+.build-logs-error { color: var(--red); }
+.build-logs-item {
+  border: 1px solid var(--border);
+  border-radius: 2px;
+}
+.build-logs-row-btn {
+  width: 100%;
+  background: none;
+  border: none;
+  color: var(--fg);
+  font-family: inherit;
+  font-size: 0.85em;
+  cursor: pointer;
+  padding: 0.35em 0.6em;
+  text-align: left;
+  display: flex;
+  gap: 0.5em;
+  align-items: center;
+  flex-wrap: wrap;
+}
+.build-logs-row-btn:hover { background: var(--bg-elev); }
+.build-logs-kind { font-weight: 600; }
+.build-logs-age  { font-size: 0.88em; }
+.build-logs-cmdline {
+  font-family: "JetBrains Mono", "Fira Code", monospace;
+  font-size: 0.8em;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  max-width: 28ch;
+}
+.build-logs-detail { padding: 0 0.4em 0.4em; }
+.build-logs-output {
+  margin: 0;
+  background: #11111b;
+  color: var(--fg);
+  border: 1px solid var(--purple-dim);
+  padding: 0.5em 0.7em;
+  overflow: auto;
+  font-size: 0.8em;
+  line-height: 1.4;
+  white-space: pre;
+  word-break: normal;
+  max-height: 60vh;
+}
+/* Status badge colours reused for build status chips. */
+.badge-ok      { background: rgba(166,227,161,0.12); color: var(--green);  border-color: var(--green); }
+.badge-fail    { background: rgba(243,139,168,0.12); color: var(--red);    border-color: var(--red);   }
+.badge-running { background: rgba(250,179,135,0.12); color: var(--amber);  border-color: var(--amber); }
+
 /* Notification controls — sit between the banner and the
    containers section. Hidden by JS when notifications are
    unsupported, denied, or already in the right state. */

frontend/packages/dashboard/src/tabs.js

@@ -709,6 +709,10 @@ window.marked = marked;
       // narrows to the harness service (or empty = full machine).
       const journalUnit = c.is_manager ? 'hive-m1nd.service' : 'hive-ag3nt.service';
       drill.append(buildJournalTrigger(c.container, journalUnit));
+      // Build-log viewer: lists recent nix build / nixos-container
+      // invocations for this agent, with click-to-expand full
+      // stdout + stderr. Backed by GET /api/build-logs/{name}.
+      drill.append(buildBuildLogsTrigger(c.name));
       // The hardcoded config-repo trigger and the agent-declared
       // extras block both moved into the unified nav strip in the
       // head row above (sourced from the agent backend via
@@ -1068,6 +1072,110 @@ window.marked = marked;
     return trigger;
   }
 
+  // Build-log viewer. Fetches the last 10 build-log headers for
+  // `agentName` from GET /api/build-logs/{agentName}, then renders
+  // a clickable list. Clicking a row fetches its full stdout+stderr
+  // from GET /api/build-logs/id/{id} and expands it inline.
+  function buildBuildLogsTrigger(agentName) {
+    const trigger = el('button', { type: 'button', class: 'panel-trigger' },
+      '↳ build logs · ' + agentName);
+    trigger.addEventListener('click', () => {
+      const panelTitle = 'build logs · ' + agentName;
+      const wrap = el('div', { class: 'build-logs-panel' });
+
+      const hdr = el('div', { class: 'build-logs-toolbar' });
+      const refreshBtn = el('button',
+        { type: 'button', class: 'btn btn-restart build-logs-refresh' },
+        '↻ refresh');
+      hdr.append(refreshBtn);
+      wrap.append(hdr);
+
+      const list = el('ul', { class: 'build-logs-list' });
+      wrap.append(list);
+
+      let fetching = false;
+
+      async function loadHeaders() {
+        if (fetching) return;
+        fetching = true;
+        list.innerHTML = '';
+        list.append(el('li', { class: 'build-logs-loading' }, 'fetching…'));
+        try {
+          const resp = await fetch('/api/build-logs/' + agentName + '?limit=10');
+          if (!resp.ok) {
+            list.innerHTML = '';
+            list.append(el('li', { class: 'build-logs-error' },
+              'error ' + resp.status + ': ' + await resp.text()));
+            return;
+          }
+          const rows = await resp.json();
+          list.innerHTML = '';
+          if (!rows || !rows.length) {
+            list.append(el('li', { class: 'build-logs-empty' }, '(no build logs yet)'));
+            return;
+          }
+          const nowUnix = Math.floor(Date.now() / 1000);
+          for (const h of rows) {
+            const li = el('li', { class: 'build-logs-item' });
+            const statusCls = h.status === 'ok' ? 'badge-ok'
+              : h.status === 'fail' ? 'badge-fail'
+              : 'badge-running';
+            const statusLabel = h.status === 'ok' ? 'ok'
+              : h.status === 'fail' ? 'fail'
+              : 'running';
+            const age = h.started_at
+              ? fmtAgeSecs(nowUnix - h.started_at) + ' ago' : '?';
+            const rowBtn = el('button',
+              { type: 'button', class: 'build-logs-row-btn' },
+              el('span', { class: `badge ${statusCls}` }, statusLabel),
+              el('span', { class: 'build-logs-kind' }, h.kind),
+              el('span', { class: 'build-logs-age meta' }, age),
+              el('span', { class: 'build-logs-cmdline meta' }, h.cmdline),
+            );
+            const detail = el('div', { class: 'build-logs-detail' });
+            detail.hidden = true;
+            let loaded = false;
+            rowBtn.addEventListener('click', async () => {
+              if (!detail.hidden) { detail.hidden = true; return; }
+              if (!loaded) {
+                detail.textContent = 'fetching…';
+                detail.hidden = false;
+                try {
+                  const r2 = await fetch('/api/build-logs/id/' + h.id);
+                  if (!r2.ok) {
+                    detail.textContent = 'error ' + r2.status + ': ' + await r2.text();
+                  } else {
+                    const full = await r2.json();
+                    const out = (full.stdout || '') + (full.stderr ? '\n--- stderr ---\n' + full.stderr : '');
+                    const pre = el('pre', { class: 'build-logs-output' }, out || '(empty)');
+                    detail.replaceChildren(pre);
+                    loaded = true;
+                  }
+                } catch (err) {
+                  detail.textContent = 'fetch failed: ' + err;
+                }
+              } else {
+                detail.hidden = false;
+              }
+            });
+            li.append(rowBtn, detail);
+            list.append(li);
+          }
+        } catch (err) {
+          list.innerHTML = '';
+          list.append(el('li', { class: 'build-logs-error' }, 'fetch failed: ' + err));
+        } finally {
+          fetching = false;
+        }
+      }
+
+      refreshBtn.addEventListener('click', loadHeaders);
+      Panel.open(panelTitle, wrap);
+      loadHeaders();
+    });
+    return trigger;
+  }
+
   function renderTombstones(s) {
     const root = $('tombstones-section');
     // #tombstones-section only lives on /index.html (SYST3M tab);