fix(causal_tree): resolve clippy violations in CTE code

- Add const fn to 22 functions (branch/engine/metrics/policy/state)
- Replace .expect() with .map_err()? in prometheus CTE metrics
- Add #[allow] to all CTE test modules (indexing_slicing etc.)
- Fix unnested or-patterns, doc indent, Debug impl, map_or
- Fix production indexing with .get().map_or() safe access

Author: g1e2x87

src/causal_tree/branch.rs

@@ -16,7 +16,7 @@ pub enum BranchLabel {
 
 impl BranchLabel {
     /// Human-readable short name for logging / tracing.
-    pub fn as_str(&self) -> &'static str {
+    pub const fn as_str(self) -> &'static str {
         match self {
             Self::DirectAnswer => "direct_answer",
             Self::RetrieveThenAnswer => "retrieve_then_answer",
@@ -139,6 +139,7 @@ pub struct PathCommitDecision {
 }
 
 #[cfg(test)]
+#[allow(clippy::indexing_slicing, clippy::unwrap_used, clippy::expect_used)]
 mod tests {
     use super::*;
 

src/causal_tree/engine.rs

@@ -74,12 +74,12 @@ impl CausalTreeEngine {
     }
 
     /// Returns `true` if the CTE is enabled in the configuration.
-    pub fn is_enabled(&self) -> bool {
+    pub const fn is_enabled(&self) -> bool {
         self.config.enabled
     }
 
     /// Returns a reference to the engine's configuration.
-    pub fn config(&self) -> &CausalTreeConfig {
+    pub const fn config(&self) -> &CausalTreeConfig {
         &self.config
     }
 
@@ -279,6 +279,7 @@ impl CausalTreeEngine {
 }
 
 #[cfg(test)]
+#[allow(clippy::indexing_slicing, clippy::unwrap_used, clippy::expect_used)]
 mod tests {
     use super::*;
     use crate::causal_tree::branch::BranchLabel;

src/causal_tree/expander.rs

@@ -43,9 +43,17 @@ fn intent_contains_any(intent: &str, keywords: &[&str]) -> bool {
                 return false;
             }
             // Check left boundary: start of string or non-alphanumeric.
-            let left_ok = i == 0 || !text_bytes[i - 1].is_ascii_alphanumeric();
+            let left_ok = i == 0
+                || text_bytes
+                    .get(i - 1)
+                    .map(|b| !b.is_ascii_alphanumeric())
+                    .unwrap_or(true);
             // Check right boundary: end of string or non-alphanumeric.
-            let right_ok = i + klen == text_bytes.len() || !text_bytes[i + klen].is_ascii_alphanumeric();
+            let right_ok = i + klen == text_bytes.len()
+                || text_bytes
+                    .get(i + klen)
+                    .map(|b| !b.is_ascii_alphanumeric())
+                    .unwrap_or(true);
             left_ok && right_ok
         })
     })
@@ -96,7 +104,7 @@ pub struct DefaultTreeExpander {
 
 impl DefaultTreeExpander {
     /// Create a new expander with its sequence counter reset to zero.
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         Self {
             seq: std::sync::atomic::AtomicU64::new(0),
         }
@@ -193,7 +201,7 @@ impl DefaultTreeExpander {
         }
         matches!(
             state.max_risk_level(),
-            Some(RiskLevel::High) | Some(RiskLevel::Critical)
+            Some(RiskLevel::High | RiskLevel::Critical)
         )
     }
 }
@@ -319,6 +327,7 @@ impl TreeExpander for DefaultTreeExpander {
 // ---------------------------------------------------------------------------
 
 #[cfg(test)]
+#[allow(clippy::indexing_slicing, clippy::unwrap_used, clippy::expect_used, clippy::needless_collect)]
 mod tests {
     use super::*;
     use crate::causal_tree::state::{BudgetState, RiskFlag};

src/causal_tree/feedback.rs

@@ -77,7 +77,7 @@ pub struct LogFeedbackWriter;
 
 impl LogFeedbackWriter {
     /// Create a new [`LogFeedbackWriter`].
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         Self
     }
 }
@@ -123,7 +123,7 @@ pub struct NoopFeedbackWriter;
 
 impl NoopFeedbackWriter {
     /// Create a new [`NoopFeedbackWriter`].
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         Self
     }
 }
@@ -145,6 +145,7 @@ impl FeedbackWriter for NoopFeedbackWriter {
 // ---------------------------------------------------------------------------
 
 #[cfg(test)]
+#[allow(clippy::indexing_slicing, clippy::unwrap_used, clippy::expect_used)]
 mod tests {
     use super::*;
     use crate::causal_tree::branch::{BranchLabel, CausalBranch, CommitPolicy, CostEstimate, RehearsalLevel};

src/causal_tree/metrics.rs

@@ -57,7 +57,7 @@ pub struct RunObservation {
 
 impl CausalTreeMetrics {
     /// Record a single CTE run observation.
-    pub fn record(&mut self, obs: &RunObservation) {
+    pub const fn record(&mut self, obs: &RunObservation) {
         self.total_runs += 1;
         if obs.hit_at_1 {
             self.hits_at_1 += 1;
@@ -78,7 +78,7 @@ impl CausalTreeMetrics {
     }
 
     /// Record a circuit breaker trip event.
-    pub fn record_circuit_breaker_trip(&mut self) {
+    pub const fn record_circuit_breaker_trip(&mut self) {
         self.circuit_breaker_trips += 1;
     }
 
@@ -138,6 +138,7 @@ impl CausalTreeMetrics {
 }
 
 #[cfg(test)]
+#[allow(clippy::indexing_slicing, clippy::unwrap_used, clippy::expect_used)]
 mod tests {
     use super::*;
 

src/causal_tree/policy.rs

@@ -74,16 +74,16 @@ pub struct CausalTreeConfig {
     pub write_metrics: bool,
 }
 
-fn default_w_confidence() -> f32 {
+const fn default_w_confidence() -> f32 {
     0.50
 }
-fn default_w_cost() -> f32 {
+const fn default_w_cost() -> f32 {
     0.25
 }
-fn default_w_latency() -> f32 {
+const fn default_w_latency() -> f32 {
     0.25
 }
-fn default_true() -> bool {
+const fn default_true() -> bool {
     true
 }
 
@@ -119,13 +119,13 @@ impl Default for CircuitBreakerState {
 
 impl CircuitBreakerState {
     /// Record a successful CTE run — resets the failure counter.
-    pub fn record_success(&mut self) {
+    pub const fn record_success(&mut self) {
         self.consecutive_failures = 0;
         self.open_since = None;
     }
 
     /// Record a failed CTE run — increments the failure counter.
-    pub fn record_failure(&mut self) {
+    pub const fn record_failure(&mut self) {
         self.consecutive_failures += 1;
     }
 
@@ -135,10 +135,8 @@ impl CircuitBreakerState {
             return false;
         }
         // If open, check whether the cooldown has elapsed.
-        match self.open_since {
-            Some(opened_at) => opened_at.elapsed().as_secs() < policy.circuit_breaker_cooldown_secs,
-            None => true,
-        }
+        self.open_since
+            .map_or(true, |opened_at| opened_at.elapsed().as_secs() < policy.circuit_breaker_cooldown_secs)
     }
 
     /// Transition to the open state if the threshold has been reached.
@@ -150,6 +148,7 @@ impl CircuitBreakerState {
 }
 
 #[cfg(test)]
+#[allow(clippy::indexing_slicing, clippy::unwrap_used, clippy::expect_used)]
 mod tests {
     use super::*;
 

src/causal_tree/rehearsal.rs

@@ -140,7 +140,7 @@ pub struct DefaultRehearsalEngine;
 
 impl DefaultRehearsalEngine {
     /// Create a new [`DefaultRehearsalEngine`].
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         Self
     }
 
@@ -247,6 +247,7 @@ impl RehearsalEngine for DefaultRehearsalEngine {
 // ---------------------------------------------------------------------------
 
 #[cfg(test)]
+#[allow(clippy::indexing_slicing, clippy::unwrap_used, clippy::expect_used)]
 mod tests {
     use super::*;
     use crate::causal_tree::{

src/causal_tree/scorer.rs

@@ -90,7 +90,7 @@ pub struct DefaultBranchScorer;
 
 impl DefaultBranchScorer {
     /// Create a new `DefaultBranchScorer`.
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         Self
     }
 
@@ -263,6 +263,7 @@ impl BranchScorer for DefaultBranchScorer {
 // ---------------------------------------------------------------------------
 
 #[cfg(test)]
+#[allow(clippy::indexing_slicing, clippy::unwrap_used, clippy::expect_used)]
 mod tests {
     use super::*;
     use crate::causal_tree::{

src/causal_tree/selector.rs

@@ -66,7 +66,7 @@ pub struct DefaultPathSelector;
 
 impl DefaultPathSelector {
     /// Create a new [`DefaultPathSelector`].
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         Self
     }
 }
@@ -149,6 +149,7 @@ impl PathSelector for DefaultPathSelector {
 // ---------------------------------------------------------------------------
 
 #[cfg(test)]
+#[allow(clippy::indexing_slicing, clippy::unwrap_used, clippy::expect_used)]
 mod tests {
     use super::*;
     use crate::causal_tree::branch::{BranchLabel, CausalBranch, CommitPolicy, CostEstimate, RehearsalLevel};

src/causal_tree/snapshot.rs

@@ -27,7 +27,7 @@ fn truncate_to_chars(s: &str, max_chars: usize) -> &str {
 }
 
 /// Map the classified [`TaskIntent`] to a human-readable intent string.
-fn intent_label(intent: TaskIntent) -> &'static str {
+const fn intent_label(intent: TaskIntent) -> &'static str {
     match intent {
         TaskIntent::Simple => "simple",
         TaskIntent::Delegate => "delegate",
@@ -86,17 +86,17 @@ fn tool_result_to_artifact(_tool_call_id: &str, content: &str, index: usize) ->
 ///
 /// # Parameters
 ///
-/// - `session_id`        — Stable session identifier (passed through).
-/// - `user_message`      — Raw user message; truncated to [`GOAL_MAX_CHARS`]
-///                         chars for the `goal` field.
-/// - `classify_result`   — Output of the task classifier; drives `user_intent`.
-/// - `history`           — Full conversation history for the current session.
+/// - `session_id`       — Stable session identifier (passed through).
+/// - `user_message`     — Raw user message; truncated to [`GOAL_MAX_CHARS`]
+///   chars for the `goal` field.
+/// - `classify_result`  — Output of the task classifier; drives `user_intent`.
+/// - `history`          — Full conversation history for the current session.
 ///   - `Chat` messages with `role == "assistant"` become completed
 ///     [`StepRecord`]s.
 ///   - `ToolResults` entries become [`ArtifactRef`]s.
-/// - `side_effect_mode`  — Current permission mode; controls `active_constraints`.
-/// - `policy`            — Active [`CausalPolicy`]; used to set the
-///                         [`BudgetState`].
+/// - `side_effect_mode` — Current permission mode; controls `active_constraints`.
+/// - `policy`           — Active [`CausalPolicy`]; used to set the
+///   [`BudgetState`].
 pub fn build_causal_state(
     session_id: &str,
     user_message: &str,
@@ -168,6 +168,7 @@ pub fn build_causal_state(
 }
 
 #[cfg(test)]
+#[allow(clippy::indexing_slicing, clippy::unwrap_used, clippy::expect_used)]
 mod tests {
     use super::super::policy::CausalPolicy;
     use super::*;