prompts: adopt compact defaults and rebalance guidance

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

plugins/_code_execution/prompts/agent.system.tool.code_exe.md

@@ -1,90 +1,26 @@
 ### code_execution_tool
-
-execute terminal commands python nodejs code for computation or software tasks
-place code in "code" arg; escape carefully and indent properly
-select "runtime" arg: "terminal" "python" "nodejs" "output"
-select "session" number, 0 default, others for multitasking
-if code runs long, use runtime "output" to wait
-use argument reset true on next call to kill previous process when stuck default false
-use "pip" "npm" "apt-get" in "terminal" to install package
-to output, use print() or console.log()
-if tool outputs error, adjust code before retrying; 
-important: check code for placeholders or demo data; replace with real variables; don't reuse snippets
-don't use with other tools except thoughts; wait for response before using others
-check dependencies before running code
-output may end with [SYSTEM: ...] information comming from framework, not terminal
-usage:
-
-
-1 execute terminal command
+run terminal, python, or nodejs commands
+args:
+- `runtime`: `terminal`, `python`, `nodejs`, or `output`
+- `code`: command or script code
+- `session`: terminal session id; default `0`
+- `reset`: kill a session before running; `true` or `false`
+rules:
+- use `runtime=output` to poll running work
+- use `input` for interactive terminal prompts
+- do not interleave other tools while waiting
+- ignore framework `[SYSTEM: ...]` info in output
+example:
 ~~~json
 {
-    "thoughts": [
-        "Need to do...",
-        "Need to install...",
-    ],
-    "headline": "Installing zip package via terminal",
-    "tool_name": "code_execution_tool",
-    "tool_args": {
-        "runtime": "terminal",
-        "session": 0,
-        "reset": false,
-        "code": "apt-get install zip",
-    }
-}
-~~~
-
-2 execute python code
-
-~~~json
-{
-    "thoughts": [
-        "Need to do...",
-        "I can use...",
-        "Then I can...",
-    ],
-    "headline": "Executing Python code to check current directory",
-    "tool_name": "code_execution_tool",
-    "tool_args": {
-        "runtime": "python",
-        "session": 0,
-        "reset": false,
-        "code": "import os\nprint(os.getcwd())",
-    }
-}
-~~~
-
-3 execute nodejs code
-
-~~~json
-{
-    "thoughts": [
-        "Need to do...",
-        "I can use...",
-        "Then I can...",
-    ],
-    "headline": "Executing Javascript code to check current directory",
-    "tool_name": "code_execution_tool",
-    "tool_args": {
-        "runtime": "nodejs",
-        "session": 0,
-        "reset": false,
-        "code": "console.log(process.cwd());",
-    }
-}
-~~~
-
-4 wait for output with long-running scripts
-~~~json
-{
-    "thoughts": [
-        "Waiting for program to finish...",
-    ],
-    "headline": "Waiting for long-running program to complete",
-    "tool_name": "code_execution_tool",
-    "tool_args": {
-        "runtime": "output",
-        "session": 0,
-    }
+  "thoughts": ["I should run a terminal command in the default session."],
+  "headline": "Running terminal command",
+  "tool_name": "code_execution_tool",
+  "tool_args": {
+    "runtime": "terminal",
+    "session": 0,
+    "reset": false,
+    "code": "pwd"
+  }
 }
 ~~~