feat(brain): surface an aging review queue in brain_context (#82)

brain_pending existed the whole time four real items sat unreviewed from
2026-04-23 to 2026-07-15. The tool was never the gap — nothing ever
prompted anyone to call it. The system should be what remembers the queue
exists.

Option 2 from the issue: ride along with brain_context, which sessions
already call, so noticing an aging note costs nobody a decision to go
looking. No scheduled job, no ntfy wiring, nothing new to keep running.

Threshold-gated at 14 days, and silent below it — a notice on every
context call is one people learn to skip, which reproduces the original
failure with extra steps. It reports the whole queue once it speaks: the
threshold decides whether to talk, not what to count.

It never promotes, rejects or reorders. Age is a reason to ask a human,
not a verdict; an old note may be exactly right to promote once someone
looks. A test asserts the queue is untouched and that the payload carries
a hint rather than an action.

An unreadable raw/ dir degrades to silence — brain_context is a hot path
and must not fail because the review queue is broken.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BeAp5LTscnz2W7Ubt4eJ6m

ingestion/internal/mcp/pending_nudge.go

@@ -0,0 +1,76 @@
+package mcp
+
+import (
+	"time"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/api"
+)
+
+// pendingNudgeThreshold is how old a raw/ note has to be before brain_context
+// mentions the queue. Two weeks: long enough that a note written this sprint
+// does not nag, short enough that four items cannot sit unnoticed for three
+// months again (#82).
+const pendingNudgeThreshold = 14 * 24 * time.Hour
+
+// PendingNudge is the in-session reminder that the promote/reject queue has
+// items waiting. It is advisory: a count, an age, and how to look.
+type PendingNudge struct {
+	Pending    int    `json:"pending"`     // everything in the queue
+	Aging      int    `json:"aging"`       // those past the threshold
+	Oldest     string `json:"oldest"`      // filename of the oldest pending note
+	OldestDays int    `json:"oldest_days"` // its age, in whole days
+	Hint       string `json:"hint"`
+}
+
+// pendingNudge summarises the raw/ review queue, or returns nil when there is
+// nothing worth saying.
+//
+// The trigger is the missing half of the queue (#82): brain_pending has always
+// existed, and four real items still sat unreviewed from 2026-04-23 to
+// 2026-07-15 because nothing ever prompted anyone to call it. The system
+// should be what remembers the queue exists.
+//
+// Threshold-gated on purpose. A notice on every context call is one people
+// learn to skip, which reproduces the original failure with extra steps.
+//
+// It never promotes, rejects, or reorders anything. Age is a reason to ask a
+// human, not a verdict — an old note may be exactly right to promote once
+// someone finally looks at it.
+func pendingNudge(brainDir string, now time.Time, threshold time.Duration) *PendingNudge {
+	pending, err := api.ListPending(brainDir)
+	if err != nil || len(pending) == 0 {
+		// brain_context is a hot path; a broken queue degrades to silence
+		// rather than failing the call that asked for project context.
+		return nil
+	}
+
+	var aging int
+	var oldestName string
+	var oldestAge time.Duration
+
+	for _, p := range pending {
+		created, perr := time.Parse(time.RFC3339, p.CreatedAt)
+		if perr != nil {
+			continue // an unparseable timestamp is not evidence of age
+		}
+		age := now.Sub(created)
+		if age >= threshold {
+			aging++
+		}
+		if age > oldestAge {
+			oldestAge, oldestName = age, p.Filename
+		}
+	}
+
+	if aging == 0 {
+		return nil
+	}
+
+	return &PendingNudge{
+		Pending:    len(pending),
+		Aging:      aging,
+		Oldest:     oldestName,
+		OldestDays: int(oldestAge.Hours() / 24),
+		Hint:       "call brain_pending to review; nothing is promoted or rejected automatically",
+	}
+}