Closes#4102.
buildPromptFromContext previously serialized multi-turn history using
literal [User] / [Assistant] / [System] bracket labels. Those tokens
are the exact pattern the anti-fabrication rule in system.md and
discuss.md forbids — the model saw its own input framed as a bracket-
labeled transcript and mirrored the format in its output, inventing
both sides of the conversation during /gsd discuss turns.
Replace the bracket labels with XML-tag structure:
- <conversation_history> wraps the whole turn sequence
- <user_message> / <assistant_message> per turn
- <prior_system_context> for the system prompt (renamed from
<system_prompt> to avoid overlap with Claude Code's reserved
<system-reminder> convention)
Prepend a directive telling the model to respond only to the final
user message and not emit the XML tags in its own response. Keep
system.md and discuss.md in sync by documenting that prior context
is delivered in those tags.
Add regression tests asserting:
- no literal [User]/[Assistant]/[System] substrings in the prompt
- history wrapped in <conversation_history> with per-turn tags
- directive leads the prompt
- empty-history edge cases still render correctly
ad2211b218