feat: agent status dashboard with availability timeline and Gemini quota detection

- Detect Gemini TerminalQuotaError (daily quota) as BUDGET_EXCEEDED, not generic FAILED
- Surface container stderr tail in error so quota/rate-limit classifiers can match it
- Add agent_events table to persist rate-limit start/recovery events across restarts
- Add GET /api/agents/status endpoint returning live agent state + 24h event history
- Stats dashboard: agent status cards, 24h availability timeline, per-run execution table

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/internal/executor/helpers.go b/internal/executor/helpers.go
index 9e4530b..aee7da0 100644
--- a/internal/executor/helpers.go
+++ b/internal/executor/helpers.go
@@ -143,6 +143,30 @@ func tailFile(path string, n int) string {
 	return strings.Join(lines, "\n")
 }
 
+// readFileTail returns the last maxBytes bytes of the file at path as a string,
+// or empty string if the file cannot be read. Used to surface agent stderr on failure.
+func readFileTail(path string, maxBytes int64) string {
+	f, err := os.Open(path)
+	if err != nil {
+		return ""
+	}
+	defer f.Close()
+	fi, err := f.Stat()
+	if err != nil {
+		return ""
+	}
+	offset := fi.Size() - maxBytes
+	if offset < 0 {
+		offset = 0
+	}
+	buf := make([]byte, fi.Size()-offset)
+	n, err := f.ReadAt(buf, offset)
+	if err != nil && n == 0 {
+		return ""
+	}
+	return strings.TrimSpace(string(buf[:n]))
+}
+
 func gitSafe(args ...string) []string {
 	return append([]string{"-c", "safe.directory=*"}, args...)
 }