fix(cache): address CR feedback — blank lines, heading hierarchy, debug_assert

- Add proper blank lines (\n\n) before mode headings in
  render_runtime_policy_reference (CommonMark/GFM compliance).
- Demote subheadings in agent.md from ##### to ###### so they
  nest correctly under the demoted main heading.
- Add debug_assert! in taxonomy_body() to loudly fail when
  render_core_tool_taxonomy_block format changes, preventing
  silent heading-hierarchy breakage.

crates/tui/src/prompts.rs

@@ -719,6 +719,12 @@ fn default_approval_mode_for_mode(mode: AppMode) -> ApprovalMode {
 /// producing a broken heading hierarchy (## under ####).
 fn taxonomy_body(mode: AppMode) -> String {
     let block = render_core_tool_taxonomy_block(mode);
+    debug_assert!(
+        block.starts_with("## Core Tool Taxonomy\n\n"),
+        "render_core_tool_taxonomy_block format changed — \
+         taxonomy_body expects `## Core Tool Taxonomy\\n\\n` prefix; \
+         update the prefix or the assertion"
+    );
     block
         .strip_prefix("## Core Tool Taxonomy\n\n")
         .unwrap_or(&block)
@@ -748,19 +754,19 @@ pub(crate) fn render_runtime_policy_reference() -> String {
 
     out.push_str("#### agent\n\n");
     out.push_str(&taxonomy_agent);
-    out.push('\n');
+    out.push_str("\n\n");
     out.push_str(AGENT_MODE.trim());
     out.push_str("\n\n");
 
     out.push_str("#### plan\n\n");
     out.push_str(&taxonomy_plan);
-    out.push('\n');
+    out.push_str("\n\n");
     out.push_str(PLAN_MODE.trim());
     out.push_str("\n\n");
 
     out.push_str("#### yolo\n\n");
     out.push_str(&taxonomy_yolo);
-    out.push('\n');
+    out.push_str("\n\n");
     out.push_str(YOLO_MODE.trim());
     out.push_str("\n\n");
 

crates/tui/src/prompts/modes/agent.md

@@ -12,7 +12,7 @@ For simple writes, state the direct edit and proceed through the normal approval
 
 For multi-step initiatives, keep `checklist_write` current. Add `update_plan` only for genuinely useful strategy.
 
-##### Efficient Approvals
+###### Efficient Approvals
 
 When your plan includes multiple writes, present them together:
 1. Show `checklist_write` with all write steps listed so the user sees the full scope
@@ -21,7 +21,7 @@ When your plan includes multiple writes, present them together:
 
 Don't sequence approvals one at a time — the user wants context, not interruption. A clear plan with visible checklist items gets approved faster than a series of surprise approval prompts.
 
-##### Session Longevity
+###### Session Longevity
 
 Long sessions accumulate context. To stay fast:
 - Open sub-agent sessions for independent work instead of doing everything sequentially