seed: mavend implements it, off unless -allow-seed (V-518)

SeedEvent writes the fact at the caller's timestamp, extracts an event from
it, and runs the same detectAndPropose the voice path runs. What a seed proves
is therefore the daemon's own wiring, not the detector in isolation — which is
what an eval-lab fixture would have proved, and is not what the four blocked
tasks doubt.

The flag is the real lock, not the authority rung. -allow-seed defaults off,
and off means daemonAPI.seedStore is nil: the method has nothing to write with
rather than permission to refuse. A box that can rewrite its own past says so
in its boot log.

Seeded facts carry source "seed:qa" and no Subject, so they never queue a
Nexus resolution and stay identifiable for the wipe in V-494. Nothing else in
the tree writes that source.

Best-effort is not the shape here, unlike detectPattern: a seed that half
worked is a QA result nobody can trust, so every step reports its own failure.
Extraction declining is not a failure, and Extracted says so.

Tests cover all four: refused with no flag, four spaced seeds propose and
three do not, a value outside the lexicon writes the fact and claims no event,
a zero timestamp is refused rather than defaulted to now.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011x5DgnExQ5XZy8TZPs5bot

cmd/mavend/tick_api.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/kami/maven/internal/ipc"
 	"github.com/kami/maven/internal/loop"
+	"github.com/kami/maven/internal/store"
 )
 
 // daemonAPI wraps a store-backed CoreAPI and overrides TickTrace with the
@@ -22,6 +23,11 @@ type daemonAPI struct {
 	chatFn           func(ctx context.Context, conversation, text string) string
 	getMCPServers    func() []ipc.MCPServerStatus
 	getEvents        func(n int) []ipc.IntakeEvent
+	// seedStore — non-nil ONLY when mavend was started with -allow-seed. It is
+	// the whole off-switch for the backdated write path (Vikunja #518), and it
+	// is a store rather than a bool so that leaving the flag off means the
+	// method has nothing to write with, not merely permission to refuse.
+	seedStore *store.Store
 }
 
 // RecentEvents — the unified intake journal (Vikunja #283). Empty, not an