docs(TASK-021): fix task-queue example IDs + document dispatch/collect/failure semantics

- prompts.rs DEFAULT_SPAWN_INSTRUCTIONS: example IDs task_1/task_2 -> "1"/"2"
  (real numeric-string IDs; old format silently produced dep_error + unblocked
  task), plus task-queue rules: root tasks with agent are never auto-dispatched,
  task_complete is what dispatches dependents, auto-dispatched agents must be
  collected, failed tasks permanently block dependents.
- architect config: optional task-queue mirroring guidance for parallel mode
  (disk task files stay the durable store; queue is in-memory).
- sisyphus config: short note on encoding dependency-shaped bursts as
  agent__task_create chains; todos remain the tracking source of truth.

src/config/prompts.rs

@@ -167,17 +167,26 @@ pub(in crate::config) const DEFAULT_SPAWN_INSTRUCTIONS: &str = indoc! {"
     ```
     # Create tasks with dependencies (optional: auto-dispatch with --agent)
     agent__task_create --subject \"Explore existing patterns\"
-    agent__task_create --subject \"Implement feature\" --blocked_by [\"task_1\"] --agent coder --prompt \"Implement based on patterns found\"
-    agent__task_create --subject \"Write tests\" --blocked_by [\"task_2\"]
+    agent__task_create --subject \"Implement feature\" --blocked_by [\"1\"] --agent coder --prompt \"Implement based on patterns found\"
+    agent__task_create --subject \"Write tests\" --blocked_by [\"2\"]
 
     # Check what's runnable
     agent__task_list
 
     # After completing a task, mark it done to unblock dependents
     # If dependents have --agent set, they auto-dispatch
-    agent__task_complete --task_id task_1
+    agent__task_complete --task_id 1
     ```
 
+    Task-queue rules (NOT obvious — read carefully):
+    - Task IDs are numeric strings (\"1\", \"2\", ...) assigned in creation order.
+    - A task created with `agent` but NO blockers is NEVER auto-dispatched — spawn it yourself.
+    - Auto-dispatch happens only inside `agent__task_complete`: completing a task is what
+      dispatches its newly-unblocked dependents.
+    - Auto-dispatched agents must still be collected via `agent__collect`, and an agent finishing
+      does NOT complete its task — call `agent__task_complete` yourself to advance the chain.
+    - A failed task permanently blocks its dependents — recreate the chain rather than retrying.
+
     ### Escalation Handling
 
     Child agents may need user input but cannot prompt the user directly. When this happens,