fix: keep post-tool final_answer brief — don't re-list tool output (closes #181) - #203

Summary

The original report: ask "list plugins", get the structured plugin list rendered as an `ability_result` UI block in the chat — but the LLM's `final_answer` text also lists every plugin again. With 20+ plugins it's pure duplication.

Two prompt nudges fix this for Qwen 3 1.7B (no new code, just better instructions to the model).

Net: +9 / -4 lines, 1 file touched.

What changed

1. `buildToolResultMessage` suffix

The message we send to the LLM right after a tool returns now ends with:

"The user already sees the tool result above — keep final_answer brief (one or two sentences). Don't re-list items the tool already returned."

(Previously just told it to call another tool or provide a final_answer, without the brevity nudge.)

2. System prompt RULES + EXAMPLE

The RULES section gained an explicit no-re-listing rule. The worked example was updated to show the desired brief style:

Before:
```json
{"action": "final_answer", "content": "You have 2 plugins: Akismet (active) and Hello Dolly (inactive)."}
```

After:
```json
{"action": "final_answer", "content": "You have 2 plugins installed. One is active."}
```

Why this is prompt-engineering, not code

The LLM can still produce a verbose answer if it wants to — these are nudges, not guarantees. Small models like Qwen 3 1.7B respond well to:

• Explicit "don't do X" rules
• Worked examples that model the desired behavior

If a user explicitly asks "list each plugin one by one and tell me what each does," the LLM should still comply — we don't want to suppress legitimate verbose responses, just the redundant restatement that happens by default.

Verification

• `npm test` — 96 passing (mock-LLM tests don't exercise prompt content directly, so no test changes)
• `composer lint` — clean
• `npx wp-scripts lint-js` — clean

This is the kind of fix that's best validated with the actual model. To test in Playground:

1. Load Qwen 3 1.7B
2. Send "list plugins" → `ability_result` renders the list
3. The text response should now be one sentence ("You have N plugins, M active") instead of a bulleted restatement

Test plan

• Build check passes
• PHP lint passes
• JS lint passes
• Unit tests pass
• Manual: "list plugins" → final_answer is brief; "list users" → same; "show me the error log" → same

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