docs: add "check available skills" playbook instruction

Teach agents to scan available skills before starting any task,
closing the escape hatch where "non-trivial" let busy agents skip.

Spec: specs/cmd-purity-cleanup.md
Signed-off-by: Jose Alekhinne <jose@ctx.ist>

Author: josealekhine

.context/AGENT_PLAYBOOK.md

@@ -122,6 +122,14 @@ is running long:
 Context compaction happens automatically, but the next window loses
 nuance. Explicit persistence is cheaper than re-discovery.
 
+### Check Available Skills
+
+Before starting any task, scan the skill list in your system
+prompt to see if a dedicated skill already handles the request.
+Prefer invoking an existing skill over ad-hoc implementation:
+skills encode project conventions, quality gates, and
+persistence steps that are easy to miss otherwise.
+
 ### Conversational Triggers
 
 Users rarely invoke skills explicitly. Recognize natural language:

.context/AGENT_PLAYBOOK_GATE.md

@@ -33,6 +33,11 @@ run tests before moving on. Track progress via TASKS.md checkboxes.
 Use the `gemini-search` MCP server for web searches. Fall back to
 built-in search only if `gemini-search` is not connected.
 
+## Check Available Skills
+
+Before starting any task, scan available skills to see if one
+already handles the request. Prefer skills over ad-hoc work.
+
 ## Conversational Triggers
 
 | User Says                                       | Action               |

.context/TASKS.md

@@ -60,7 +60,7 @@ TASK STATUS LABELS:
   compliance_test.go for the full list. #priority:medium #added:2026-03-31-005115
 
 
-- [ ] PD.4.5: Update AGENT_PLAYBOOK.md — add generic "check available skills"
+- [x] PD.4.5: Update AGENT_PLAYBOOK.md — add generic "check available skills"
   instruction #priority:medium #added:2026-03-25-203340
 
 **PD.5 — Validate:**