fix: resolve deferred review items from PRs #883, #848, #788 (#915)

Address three deferred implementation items flagged during code review:

1. SIGHUP lock held across .await (#883): Split restart_with_addr into
   merged_router_clone() + install_listener() so the async TcpListener
   bind happens outside the mutex, eliminating lock contention risk.

2. Recursion depth limit for check_strings (#848): Cap JSON traversal
   at 32 levels to prevent stack overflow on pathological tool params.

3. Named error type for add_tokens (#788): Replace Result<(), String>
   with TokenBudgetExceeded { used, limit } for type-safe budget errors.

Co-authored-by: Claude Opus 4.6 <[email protected]>

src/context/mod.rs

@@ -12,4 +12,4 @@ mod state;
 
 pub use manager::ContextManager;
 pub use memory::{ActionRecord, ConversationMemory, Memory};
-pub use state::{JobContext, JobState, StateTransition};
+pub use state::{JobContext, JobState, StateTransition, TokenBudgetExceeded};

src/context/state.rs

@@ -11,6 +11,16 @@ use uuid::Uuid;
 
 use crate::llm::recording::HttpInterceptor;
 
+/// Error returned when a job exceeds its token budget.
+#[derive(Debug, thiserror::Error)]
+#[error("Token budget exceeded: used {used} of {limit} allowed tokens")]
+pub struct TokenBudgetExceeded {
+    /// Total tokens consumed (including the call that exceeded the budget).
+    pub used: u64,
+    /// Configured token limit for this job.
+    pub limit: u64,
+}
+
 /// State of a job.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
@@ -265,15 +275,15 @@ impl JobContext {
         self.actual_cost += cost;
     }
 
-    /// Record token usage from an LLM call. Returns an error string if the
-    /// token budget has been exceeded after this addition.
-    pub fn add_tokens(&mut self, tokens: u64) -> Result<(), String> {
+    /// Record token usage from an LLM call. Returns an error if the token
+    /// budget has been exceeded after this addition.
+    pub fn add_tokens(&mut self, tokens: u64) -> Result<(), TokenBudgetExceeded> {
         self.total_tokens_used += tokens;
         if self.max_tokens > 0 && self.total_tokens_used > self.max_tokens {
-            Err(format!(
-                "Token budget exceeded: used {} of {} allowed tokens",
-                self.total_tokens_used, self.max_tokens
-            ))
+            Err(TokenBudgetExceeded {
+                used: self.total_tokens_used,
+                limit: self.max_tokens,
+            })
         } else {
             Ok(())
         }