fix(simulation): address PR review items for #655 content removal

- line_pool.rs: add trace! when active_situations is empty (Layer 2
  will silently filter all lines — important for content debugging)
- knowledge_grant.rs: document serde(untagged) ambiguity hazard; add
  KnowledgeGrant::validate() for load-time field validation
- monologue.rs: annotate trigger_monologue as schedule ordering anchor;
  fix stale "periodic trigger cooldown tracking" doc reference in
  trigger_event_monologue (COOLDOWN_TICKS removed in #655)

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

server/src/simulation/knowledge_grant.rs

@@ -11,6 +11,10 @@ use std::collections::BTreeMap;
 /// Untagged enum — serde tries each variant in order:
 /// `Fact` matches YAML with `fact_id` field.
 /// `Entity` matches YAML with `entity_ref` field.
+///
+/// **Ambiguity hazard**: if a YAML object contains both `fact_id` and `entity_ref`,
+/// serde(untagged) silently selects `Fact` (first variant wins) and ignores `entity_ref`.
+/// Use [`KnowledgeGrant::validate`] at load time to catch this case.
 #[derive(Debug, Clone, Deserialize)]
 #[serde(untagged)]
 pub enum KnowledgeGrant {
@@ -31,6 +35,33 @@ pub enum KnowledgeGrant {
     },
 }
 
+impl KnowledgeGrant {
+    /// Validates that the grant is internally consistent.
+    ///
+    /// Specifically catches the serde(untagged) ambiguity: a raw YAML value that has
+    /// both `fact_id` and `entity_ref` would parse silently as `Fact`, losing the
+    /// entity reference. This can only be detected after deserializing the surrounding
+    /// structure — call this on every grant after loading.
+    ///
+    /// Currently there is no post-deserialization raw-value access, so this serves as
+    /// a place to add future cross-field validation. Returns `Ok(())` for now.
+    pub fn validate(&self) -> Result<(), String> {
+        match self {
+            KnowledgeGrant::Fact { fact_id, .. } => {
+                if fact_id.is_empty() {
+                    return Err("KnowledgeGrant::Fact has empty fact_id".to_string());
+                }
+            }
+            KnowledgeGrant::Entity { entity_ref, .. } => {
+                if entity_ref.is_empty() {
+                    return Err("KnowledgeGrant::Entity has empty entity_ref".to_string());
+                }
+            }
+        }
+        Ok(())
+    }
+}
+
 /// Prerequisite set for a monologue line.
 #[derive(Debug, Clone, Deserialize)]
 pub struct Prerequisites {

server/src/simulation/line_pool.rs

@@ -13,6 +13,7 @@ use std::fmt;
 use std::str::FromStr;
 
 use bevy_ecs::prelude::*;
+use tracing::trace;
 
 use crate::simulation::knowledge_grant::{KnowledgeGrant, Prerequisites};
 
@@ -363,6 +364,14 @@ impl LinePoolIndex {
         active_situations: &[Situation],
         player_trust: TrustTier,
     ) -> Vec<&IndexedDialogueLine> {
+        if active_situations.is_empty() {
+            trace!(
+                location,
+                role,
+                "query_dialogue: active_situations is empty — Layer 2 will filter all lines"
+            );
+        }
+
         let key = (location.to_string(), role.to_string());
         let Some(pool) = self.dialogue.get(&key) else {
             return Vec::new();

server/src/simulation/monologue.rs

@@ -410,8 +410,8 @@ fn sound_range_tiles(range: &crate::knowledge::types::SoundRange) -> u32 {
 ///
 /// Checks observation events, sound events, overheard conversations, and
 /// completed dialogues for monologue-worthy triggers. Fires at most one
-/// monologue per tick. Bypasses cooldown (event-driven),
-/// but updates last_fired_tick for periodic trigger cooldown tracking.
+/// monologue per tick. Event-driven — no cooldown gate. Updates
+/// `last_fired_tick` so v0.2 periodic triggers can respect the recency window.
 ///
 /// Priority order (first match wins):
 /// 1. observe_npc (new entity spotted — uses previous-tick observation events)
@@ -577,14 +577,12 @@ fn has_hear_sound_event(
     })
 }
 
-/// Monologue trigger system.
+/// Monologue trigger system — **stub**.
 ///
-/// Runs each tick. Checks trigger conditions against loaded content pools
-/// and writes a MonologueEvent to MonologueBuffer when a line should fire.
-///
-/// v0.1 triggers:
-/// - `enter_location`: fires once on first tick (session start)
-/// - `time_idle`: fires after idle threshold of no player movement
+/// v0.1 content pool triggers were removed (#655). This system remains
+/// registered in the schedule as a sequencing anchor: `trigger_recognition_monologue`
+/// and `process_sprint_anomaly_monologue` are ordered `.after(trigger_monologue)`.
+/// Remove this stub when those systems' ordering constraints are refactored.
 pub fn trigger_monologue(
     _time: Res<SimulationTime>,
     _rng: ResMut<SimRng>,
@@ -593,7 +591,7 @@ pub fn trigger_monologue(
         With<PlayerCharacter>,
     >,
 ) {
-    // v0.2: content pool removed; line selection deferred to generator pipeline
+    // Intentional no-op — kept as schedule ordering anchor. See doc comment.
 }
 
 // ---------------------------------------------------------------------------