fix: avoid opencode structured output session breakage

Replace server-enforced structured output with local JSON parsing for Git generation
Render generated commit and PR JSON responses as compact chat cards
Tighten generation prompts while preserving active session context

packages/ui/src/lib/magicPrompts.ts

@@ -60,7 +60,9 @@ export const MAGIC_PROMPT_DEFINITIONS: readonly MagicPromptDefinition[] = [
     placeholders: [
       { key: 'selected_files', description: 'Bullet list of currently selected file paths.' },
     ],
-    template: `Return JSON with exactly this shape:
+    template: `Return exactly one JSON object and nothing else. Do not include prose, markdown, explanations, or code fences.
+
+The JSON object must have exactly this shape:
 {"subject": string, "highlights": string[]}
 
 Rules:
@@ -69,6 +71,8 @@ Rules:
 - no scope in subject
 - keep subject concise and user-facing
 - highlights: 0-3 concise user-facing points
+- use double quotes for all JSON strings
+- do not include trailing commas or comments
 
 Selected files:
 {{selected_files}}`,
@@ -92,13 +96,18 @@ Selected files:
       { key: 'changed_files', description: 'Bullet list of changed files in base...head.' },
       { key: 'additional_context_block', description: 'Optional Additional context block (already formatted).' },
     ],
-    template: `Return JSON with exactly this shape:
+    template: `Return exactly one JSON object and nothing else. Do not include prose, markdown outside JSON, explanations, or code fences.
+
+The JSON object must have exactly this shape:
 {"title": string, "body": string}
 
 Rules:
 - title: concise, outcome-first, conventional style
 - body: markdown with sections: ## Summary, ## Why, ## Testing
 - keep output concrete and user-facing
+- put all markdown inside the body string
+- use double quotes for all JSON strings and escape newlines as \\n
+- do not include trailing commas or comments
 
 Base branch: {{base_branch}}
 Head branch: {{head_branch}}