fix: harden gossip, HLC restarts, watcher races, MCP args, pagination

- gossip: validate push batches (4 MiB / 1000-row caps); reject rows
  claiming the local node id (vector-poisoning), empty ids, negative HCLs
- gossip: reconcile derived state after pulls (pulls only append to the
  observation log, so entry-count comparison could never trigger it)
- hlc: seek clock from persisted MAX(hcl) at Open so a restart with a
  regressed wall clock cannot reissue values (locator/cursor safety)
- db: serialize writers via BEGIN IMMEDIATE DSN, single conn per pool,
  and a per-KnoxDB mutex around RecordObservation's dedup
- watch: atomic ticker guards (was a cross-goroutine data race),
  trailing-edge per-path debounce, recursive directory watches,
  rename re-ingest, remove cancels pending ingests
- mcp: strict argument validation (no silent clamping), thread existence
  checks before writes, nil-safe golden-thread tool
- cli: --page 0 no longer panics; query/recent pagination actually pages
- tests: hlc SeekTo monotonicity, concurrent dedup race, push validation,
  batch caps, idempotency on observation counts

internal/db/gossip.go

@@ -3,6 +3,7 @@ package db
 import (
 	"database/sql"
 	"fmt"
+	"log"
 )
 
 // GossipObservation is the serializable wire form of an observation exchanged
@@ -40,6 +41,19 @@ func (k *KnoxDB) PushObservations(rows []GossipObservation) (int, error) {
 
 	inserted := 0
 	for _, o := range rows {
+		// Reject malformed or forged rows. Nodes only ever push their own
+		// observations, so a row claiming this node's id cannot be legitimate:
+		// accepting it would let a peer poison our knowledge vector (a forged
+		// max-HCL makes peers believe they have our whole history and stop
+		// pulling). Empty node ids and negative HCLs are likewise never produced
+		// by a real node.
+		if o.NodeID == "" || o.HCL < 0 {
+			continue
+		}
+		if o.NodeID == k.nodeID {
+			log.Printf("[gossip] dropped pushed row claiming local node_id (spoof?)")
+			continue
+		}
 		res, err := tx.Exec(
 			`INSERT OR IGNORE INTO observations
 			 (fingerprint, source_id, source_path, project, content_type, title, summary,