strengthen AI duplicate prevention with hierarchical context

- build_triage_context now shows subtasks indented under parents so
  the AI can see the full hierarchy before deciding create vs update
- added CRITICAL deduplication rules to triage system prompt
- strengthened create_task/update_task tool descriptions to prefer
  updates over creating duplicates
- increased context limit from 40 to 60 to accommodate subtask lines

Co-Authored-By: Warp <agent@warp.dev>

Author: ComputelessComputer

src/llm.rs

@@ -1149,7 +1149,7 @@ fn triage_tool_defs(provider: Provider, bucket_names: &[String]) -> serde_json::
         make_tool_def(
             provider,
             "create_task",
-            "Create a new task. Use when the user describes genuinely new work.",
+            "Create a new task. Use ONLY when the user describes genuinely new work that does NOT overlap with any existing task or sub-task. Always check existing tasks first.",
             json!({
                 "type": "object",
                 "properties": {
@@ -1176,7 +1176,7 @@ fn triage_tool_defs(provider: Provider, bucket_names: &[String]) -> serde_json::
         make_tool_def(
             provider,
             "update_task",
-            "Update an existing task. Use for status changes, field updates, or adding sub-tasks.",
+            "Update an existing task. PREFER this over create_task when similar work already exists. Use for status changes, field updates, or adding sub-tasks.",
             json!({
                 "type": "object",
                 "properties": {
@@ -1323,6 +1323,11 @@ fn triage_task(cfg: &LlmConfig, job: &AiJob, raw_input: &str) -> AiResult {
     let system = "You are an expert AI project manager. Analyze the user's message and call \
         the appropriate tool.\n\
         Rules:\n\
+        - CRITICAL: Before creating ANY task, carefully check ALL existing tasks AND their sub-tasks \
+        (lines starting with ↳). If a task or sub-task with similar meaning already exists, use \
+        update_task instead of create_task. NEVER create a duplicate.\n\
+        - When adding sub-tasks, check the parent's existing sub-tasks first. Do NOT create sub-tasks \
+        that overlap with ones already listed.\n\
         - Generate clean, actionable titles (do NOT use the user's raw words verbatim).\n\
         - Infer progress from context (e.g. \"already working on X\" → \"In progress\").\n\
         - If the user asks to break down, decompose, split, or create sub-tasks, use decompose_task.\n\

src/main.rs

@@ -2868,12 +2868,20 @@ fn build_ai_context(tasks: &[Task]) -> Vec<llm::ContextTask> {
 }
 
 /// Build rich context for triage: full task details so the AI can match intent.
+/// Shows parent tasks with their sub-tasks indented to expose the full hierarchy.
 fn build_triage_context(tasks: &[Task]) -> String {
-    let mut refs: Vec<&Task> = tasks.iter().collect();
-    refs.sort_by(|a, b| b.updated_at.cmp(&a.updated_at));
+    // Collect parent (root) tasks sorted by recency.
+    let mut parents: Vec<&Task> = tasks.iter().filter(|t| t.parent_id.is_none()).collect();
+    parents.sort_by(|a, b| b.updated_at.cmp(&a.updated_at));
 
     let mut out = String::new();
-    for t in refs.iter().take(40) {
+    let mut count = 0usize;
+    let limit = 60;
+
+    for t in &parents {
+        if count >= limit {
+            break;
+        }
         let short = t.id.to_string().chars().take(8).collect::<String>();
         let desc = if t.description.trim().is_empty() {
             ""
@@ -2893,6 +2901,36 @@ fn build_triage_context(tasks: &[Task]) -> String {
                 desc
             }
         ));
+        count += 1;
+
+        // Show children indented under their parent.
+        let children = children_of(tasks, t.id);
+        for &idx in &children {
+            if count >= limit {
+                break;
+            }
+            let child = &tasks[idx];
+            let child_short = child.id.to_string().chars().take(8).collect::<String>();
+            let child_desc = if child.description.trim().is_empty() {
+                ""
+            } else {
+                child.description.trim()
+            };
+            out.push_str(&format!(
+                "  ↳ {} [{}] {} | {} | {} | {}\n",
+                child_short,
+                child.bucket,
+                child.title,
+                child.progress.title(),
+                child.priority.title(),
+                if child_desc.is_empty() {
+                    "no description"
+                } else {
+                    child_desc
+                }
+            ));
+            count += 1;
+        }
     }
     out
 }