feat: prominent failure-reason block + heuristic in drawer (1.0.0-50)

When a stage ends in failed/cancelled/unknown the drawer now shows
a coloured "Reason" pill at the top of that stage's section. Three
sources, in order of preference:

1. stage.error_text (the canonical, when set)
2. job.error_text (backfilled in the drawer endpoint when stage's
   own is empty — catches orphan rows from hard crashes like the
   pre-busy-timeout DB-locked failures)
3. Heuristic: if log_text is tiny (<500 bytes, just the START
   banner) AND no real badblocks progress was recorded, label as
   "Stopped without recording an error — likely cause: SSH
   connection drop or container restart while this stage was
   running." This catches the fingerprint of a deploy-during-burn-in
   killing the SSH session.

Otherwise: "No error message recorded." so there's never a blank
where the operator expects to see why something broke.

Red styling for failed, yellow for cancelled/unknown. Replaces the
inline stage-error-line for terminal states; the existing
stage-error-line still renders for non-terminal contexts.

app/config.py

@@ -86,7 +86,7 @@ class Settings(BaseSettings):
     ssh_key: str = ""             # PEM private key content (paste full key including headers)
 
     # Application version — used by the /api/v1/updates/check endpoint
-    app_version: str = "1.0.0-49"
+    app_version: str = "1.0.0-50"
 
     # ---- Authentication (1.0.0-22) ----
     # session_secret: HMAC key for signing session cookies. Empty = generate

app/routes/drives.py

@@ -62,7 +62,21 @@ async def drive_drawer(drive_id: int, db: aiosqlite.Connection = Depends(get_db)
             "FROM burnin_stages WHERE burnin_job_id=? ORDER BY id",
             (job_row["id"],),
         )
-        job["stages"] = [dict(r) for r in await cur.fetchall()]
+        stages = [dict(r) for r in await cur.fetchall()]
+        # Backfill empty stage.error_text from the parent job's error_text
+        # for any stage that ended in a terminal state without recording
+        # an error of its own. This catches the orphan pattern from hard
+        # crashes (DB-locked, SSH disconnect, container restart) where
+        # the failure didn't get to write a per-stage explanation.
+        job_err = job.get("error_text")
+        for s in stages:
+            if (
+                s.get("state") in ("failed", "cancelled", "unknown")
+                and not s.get("error_text")
+                and job_err
+            ):
+                s["error_text"] = job_err
+        job["stages"] = stages
         burnin_job = job
 
     # SMART raw output from smart_tests table

app/static/app.css

@@ -2896,3 +2896,46 @@ th.sort-desc::after {
   opacity: 1;
   border-top: 5px solid var(--blue, #58a6ff);
 }
+
+/* -----------------------------------------------------------------------
+   Stage "Reason" block — explains why a stage ended in a terminal
+   state. Replaces the old single-line stage-error-line for
+   failed/cancelled/unknown stages so the operator gets a clear,
+   prominent explanation at the top.
+----------------------------------------------------------------------- */
+.stage-reason {
+  display: flex;
+  gap: 10px;
+  align-items: baseline;
+  padding: 8px 12px;
+  margin: 6px 0;
+  border-radius: 5px;
+  font-size: 12px;
+  border: 1px solid;
+}
+.stage-reason-failed {
+  background: var(--red-bg, color-mix(in srgb, var(--red) 12%, transparent));
+  border-color: var(--red-bd, color-mix(in srgb, var(--red) 40%, transparent));
+}
+.stage-reason-cancelled,
+.stage-reason-unknown {
+  background: var(--yellow-bg, color-mix(in srgb, var(--yellow) 12%, transparent));
+  border-color: var(--yellow-bd, color-mix(in srgb, var(--yellow) 40%, transparent));
+}
+.stage-reason-label {
+  font-size: 10px;
+  text-transform: uppercase;
+  letter-spacing: .06em;
+  font-weight: 600;
+  color: var(--text-muted);
+  flex-shrink: 0;
+}
+.stage-reason-text {
+  flex: 1;
+  color: var(--text-strong, #f0f6fc);
+  line-height: 1.4;
+  word-wrap: break-word;
+}
+.stage-reason-failed .stage-reason-text { color: var(--red, #f85149); }
+.stage-reason-cancelled .stage-reason-text,
+.stage-reason-unknown .stage-reason-text { color: var(--yellow, #d29922); }

app/static/app.js

@@ -1564,7 +1564,27 @@
           html += '<span class="stage-duration">' + _drawerFmtDuration(s.started_at, s.finished_at) + '</span>';
         }
         html += '</div>';
-        if (s.error_text) {
+        // Prominent "Why it failed" block at the top of failed/cancelled/
+        // unknown stages. Falls back to a heuristic when no error was
+        // recorded — e.g. a tiny log + no badblocks progress + terminal
+        // state means the stage was killed externally (SSH disconnect or
+        // container restart) before it could record an error.
+        if (s.state === 'failed' || s.state === 'cancelled' || s.state === 'unknown') {
+          var reason = s.error_text;
+          if (!reason) {
+            var logLen = (s.log_text || '').length;
+            var noBbProgress = !s.bb_phase || (s.bb_phase === 1 && (parseFloat(s.bb_phase_pct || 0) < 0.1));
+            if (logLen < 500 && noBbProgress) {
+              reason = 'Stopped without recording an error — likely cause: SSH connection drop or container restart while this stage was running.';
+            } else {
+              reason = 'No error message recorded.';
+            }
+          }
+          html += '<div class="stage-reason stage-reason-' + _esc(s.state) + '">';
+          html += '<span class="stage-reason-label">Reason</span>';
+          html += '<span class="stage-reason-text">' + _esc(reason) + '</span>';
+          html += '</div>';
+        } else if (s.error_text) {
           html += '<div class="stage-error-line">' + _esc(s.error_text) + '</div>';
         }
         // Per-pattern meters for badblocks surface_validate, plus the