Promote the a0_small prompt work into the shipped default stack.
Token count for default prompt, accounting for tools, plugins, secrets placeholders, inactive project, etc: 2996 tokens.
- migrate compact prompt fragments into core prompts, plugin-owned prompts, and the agent0 overlay
- remove the obsolete a0_small profile and rename the tool-call knowledge reference to a generic framework file
- keep a small set of high-value JSON examples while preserving key guardrails for tool names, tool args, and method-style calls
- bake balanced conciseness into default response behavior without changing the initial greeting
- drop the call_sub prompt-side loader and keep call_sub guidance self-contained
- restore essential secrets/security guidance, preserve inactive-project messaging, and rebalance the A2A prompt
- add a regression test that verifies the assembled default agent0 prompt stays under the token budget and retains critical guardrails
