Deduplicate ACP thread prompt context

[salman1993]

Why

This is a small isolated follow-up to #6503: remove two proven duplicate prompt fragments without adopting its broader framing experiment or changing Buzz-native routing and identity behavior.

What

• Remove parsed parent=<id> only when it exactly duplicates parsed root=<id>; retain root=<id>, nested parents where parent differs from root, raw event tags, event IDs, author identity, mention fields and rules, and the explicit --reply-to instruction.
• Remove the full-history retrieval hint only when complete, untruncated conversation or thread context is included. Thread context must include its root and cover every event rendered in the batch; mixed-thread batches and root-missing windows retain retrieval guidance. Context that is absent, previously delivered, or truncated also retains retrieval guidance, and the context header, count, and messages remain unchanged.

Risk Assessment

Low — the change is confined to Buzz ACP prompt rendering and preserves all routing, identity, event, and retrieval information outside the two exact duplicate cases.

Testing

• cargo test -p buzz-acp — 804 unit tests and 9 lifecycle integration tests passed on the clean rerun
• Focused mixed-thread, same-thread, and missing-root prompt regressions passed
• The timing-sensitive keepalive_resets_idle_past_deadline test passed in isolation after one unrelated full-suite flake, then passed in the clean full rerun
• cargo clippy -p buzz-acp --all-targets -- -D warnings
• cargo fmt --all -- --check
• just file-size-check
• Repository pre-push gate at 1b88793574e74e22f00a1fd19bfe9aa8e86150fa — file-size, branch, Rust unit-test, and Desktop Tauri lanes passed
• git diff --check

Generated with Codex

[salman1993]

🤖 Re-review at exact head 1b88793574e74e22f00a1fd19bfe9aa8e86150fa: approved — no actionable findings.

The prior mixed-thread and missing-root blockers are fixed. The retrieval hint is now omitted only when the fetched window is untruncated, includes the thread root where applicable, covers every rendered batch/cancelled event, and contains no previously delivered events. Mixed-thread, reply-only, truncated, absent, and delivery-delta cases keep the escape hatch. parent is removed only when it equals root; nested parents, raw tags, event IDs, identity/mentions, and reply routing remain.

Validation:

• Independently verified by FastValidator: full cargo test -p buzz-acp (804 unit + 9 lifecycle passed), clippy, and fmt at this SHA.
• Independently rechecked here: the four focused regressions pass; git diff --check is clean.
• Live-local pass against a fresh database and relay built at this SHA: a real thread root + prior reply + live reply reached a scripted ACP through session/prompt; the prompt retained root/history/raw tags/routing, omitted duplicate parent, and omitted the retrieval hint for that complete same-thread turn.
• CI's Unit Tests job is red only because buzz-voice cannot link sherpa-onnx-c-api; the same failure is present on a later unrelated main run (32783072355). All other PR checks are green.

Product fit: this remains the narrow deletion-oriented follow-up to closed #6503 and aligns with VISION_AGENT.md's minimal/auditable boundary without adopting the broader envelope framing.

Quality bar: minimalness 9/10, elegance 9/10, correctness 9/10.

[atishpatel]

Reviewed exact head 5b581d682c15358bd92dfabeaa7c08e4c435eb04: approved — no actionable findings.

I traced both deletion conditions through the fetch/delivery-delta/rendering path. The retrieval escape hatch remains for truncated or root-missing windows, mixed-thread/cancelled batches, and any context containing previously delivered events; it is omitted only when the context plus rendered batch covers the full conversation. Direct replies drop only the redundant parsed parent while preserving root, nested parents, raw tags, event identity, mentions, and reply routing.

Independent validation on a dedicated clean worktree at this SHA:

• cargo test -p buzz-acp: 804 unit + 9 lifecycle tests passed
• cargo clippy -p buzz-acp --all-targets -- -D warnings: passed
• cargo fmt --all -- --check: passed
• Mutation check: removing the missing-root completeness guard was caught by test_thread_context_retrieval_hint_only_when_needed
• GitHub checks are green

[wpfleger96]

🤖 Combined review from the Buzz agent team (two independent source reviews + live E2E verification), at head ded2c7d.

Source review (two independent passes, convergent):

• parent=<id> omission is gated on exact equality with the parsed root via the shared NIP-10 resolver; nested parents, raw tags, event IDs, author identity, mentions, and the explicit --reply-to instruction all survive. No information loss — the raw Tags: array still carries everything.
• The retrieval-hint omission is conservative on every seam probed: Complete requires an untruncated window, root_present, full batch coverage (including cancelled events), and no prior-session deliveries. Adversarial edges hold — root previously delivered, root itself in the batch (delta strips it as a triggering event, but the root's missing e-tag fails the coverage check so the hint is retained), reply-bearing DM batches, and the truncated-count race (fetch_thread_total clamps to the sentinel minimum).
• root_present is derived at parse time in both response paths and carried intact through conversation_context_delta — no path fabricates completeness.

Live E2E (headless, real CLI → relay → buzz-acp → ACP wire capture): direct reply, nested reply, 14-message truncated chain, and follow-up-turn delivery-delta cases all behaved exactly as the PR describes — duplicate parent= and the hint absent only in the proven-complete cases, retained everywhere else.

No findings. Approving.