feat: inject background-jobs prompt guidance when jobs are enabled

Agents whose function pool includes job__* declarations get a Background
Jobs section teaching start/check/collect/cancel discipline and the
snapshot/no-persistence semantics. Presence of the declarations doubles
as the jobs_enabled predicate, so a context with function calling off or
max_concurrent_jobs 0 sees no job prompt text.

src/config/agent.rs

@@ -3,15 +3,19 @@ use super::*;
 use crate::{
     client::Model,
     config::memory,
-    function::{Functions, jobs::DEFAULT_MAX_CONCURRENT_JOBS, run_llm_function},
+    function::{
+        Functions,
+        jobs::{DEFAULT_MAX_CONCURRENT_JOBS, JOB_FUNCTION_PREFIX},
+        run_llm_function,
+    },
     graph, rag,
 };
 
 use super::rag_cache::RagKey;
 use crate::config::paths;
 use crate::config::prompts::{
-    DEFAULT_SPAWN_INSTRUCTIONS, DEFAULT_TEAMMATE_INSTRUCTIONS, DEFAULT_TODO_INSTRUCTIONS,
-    DEFAULT_USER_INTERACTION_INSTRUCTIONS,
+    DEFAULT_JOB_INSTRUCTIONS, DEFAULT_SPAWN_INSTRUCTIONS, DEFAULT_TEAMMATE_INSTRUCTIONS,
+    DEFAULT_TODO_INSTRUCTIONS, DEFAULT_USER_INTERACTION_INSTRUCTIONS,
 };
 use crate::graph::types::RagNode;
 use crate::graph::{Graph, GraphParser, NodeType};
@@ -450,6 +454,17 @@ impl Agent {
             output.push_str(DEFAULT_SPAWN_INSTRUCTIONS);
         }
 
+        // Job declarations are appended at init iff jobs are enabled for this
+        // agent, so their presence doubles as the jobs_enabled predicate.
+        if self
+            .functions
+            .declarations()
+            .iter()
+            .any(|f| f.name.starts_with(JOB_FUNCTION_PREFIX))
+        {
+            output.push_str(DEFAULT_JOB_INSTRUCTIONS);
+        }
+
         output.push_str(DEFAULT_TEAMMATE_INSTRUCTIONS);
         output.push_str(DEFAULT_USER_INTERACTION_INSTRUCTIONS);