chore(agent): phase roadmap from TODO.md — 6 phases (111–116): banner retry, honesty gate, chip quality, embed length, draft discard, modal scrollbar

.agents/phases/todo/113_source_chip_quality/00_phase.md

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+# Phase 113 — Source chip quality: usefulness bar + related-docs tier (TODO L5 + L2c)
+
+**Source:** `TODO.md` L101–147 — "L5 — Recurring weak-hit source chips: the 2nd chip is often noise the answer never used (2026-09-15, brain-of-reese interactive test)" — root-cause chain (L125–129), suggested directions (L131–142), acceptance (L144–146) — plus `TODO.md` L57–62 (L2 part c): "c) **Misleading chips on non-grounded answers** (`chat.py:252` — `done.sources` = weak hits when deflected; by design, but visually a citation). … At minimum: never render them as answer citations."
+**Story:** n/a (interactive-test follow-up fix; extends the phase-09 retrieval-quality and phase-05 chip assets).
+**Context:** `top_n_docs = 2` (`app/config.py:114`) forces two docs into `plan.docs`; `done.sources` (`app/api/chat.py` ~L796, `ChatDoneEvent.sources`) carries every entry and `appendSources` (`frontend/assets/app.js:1369`) chips them all with identical visual weight — "the answer used this" vs "this also scored" is indistinguishable. Deflected turns carry weak hits in `sources` "by design" but they render as citations. Owner-confirmed direction: the deterministic **usefulness bar** (server-side) + the **visual split** (UI) — cite-gated chips (parsing the model's cited paths) are rejected for now (stochastic with a small model).
+
+## Objective
+A document earns a citation slot only when its retrieval signal is vector-corroborated (or the agent explicitly read it via a tool call); everything else that scored is demoted to a clearly secondary "nearby docs" row that never reads as a citation. For a single-document question the turn shows exactly one citation chip; a deflected turn shows no citation chips at all.
+
+## Dependencies
+- `112_honesty_gate_weak_hits` (todo) — the gate fix stops weak hits being injected into the HIGH prompt; this phase stops weak docs earning a `done.sources` slot. Same workstream, ordered after the gate.
+
+## Design (shared by all tasks — the executor reads this, not the chat)
+- **Usefulness bar (task 01):** new settings `source_usefulness_floor: float = 0.35` (env `BOR_SOURCE_USEFULNESS_FLOOR`, validated `0 <= floor <= relevance_threshold`, mirroring phase 112's floor) and `related_max_docs: int = 2` (env `BOR_RELATED_MAX_DOCS`, validated `>= 0`). In `plan_turn`, retrieval docs are tiered: **cited** = distinct parent docs (best fused-score order, at most `top_n_docs`) whose best hit-chunk **cosine** clears the floor; **related** = the next scored distinct docs (at most `related_max_docs`) that did not clear it. Agent-read docs (`holder.read_docs`, the phase-37 agent tool reads) always stay cited — the model read them via tool calls, so they were used by definition. `TurnPlan` gains `related_docs: list[Document] = []`; the tiering is a new `select_documents_tiered(chunks, n, floor, related_cap) -> tuple[list[Document], list[Document]]` in `app/rag/retriever.py`, with `select_documents` becoming a thin wrapper (legacy behavior byte-identical for existing callers/tests). `query_log.sources` is unchanged (it records retrieval, not citations — locked A3).
+- **Done frame (task 01):** `ChatDoneEvent` (`app/schemas.py`) gains `related: list[SourceRef] = []` — additive; old clients ignore unknown fields (house contract, PLAN §4). Built from `plan.related_docs` with the same (source, path) dedupe against the cited list as `cited_docs` already does.
+- **UI split (task 02):** `frontend/assets/app.js` — new `appendRelated(wrap, related)` renders a `.msg-meta.related-docs` row under the bubble (only when `related` is non-empty): a small de-emphasized label "Nearby docs, in case:" + one link per doc with the class `related-doc` (NOT `source-chip`) — same `documentUrl(...)` href and left-click → `openDocumentModal` behavior as citation chips, visually secondary (reduced opacity/size/dashed border via theme variables; link contrast ≥4.5:1, WCAG 2.1 AA). The done-frame handler (~L2421) also calls `appendRelated(wrap, ev.related)`; the restored-chat path (~L1561) likewise when the stored payload carries `related` (pre-phase chats don't — graceful). Deflected turns: `ev.sources` is empty (the server change) → no chips; the weak hits arrive in `ev.related` → the row only.
+- **NOT touched:** the citation-chip component (`.source-chip` / `appendSources`) for the cited tier; the suggestion chips; `top_n_docs` (ceiling, not quota); the phase-37 agent-read dedupe; the Sources/RAG pages.
+
+## Tasks
+1. `01_usefulness_bar_sources.md` — retriever tiering + `TurnPlan.related_docs` + `ChatDoneEvent.related` + the two settings.
+2. `02_secondary_related_docs_ui.md` — the related-docs row in the chat UI (app.js + styles.css); deflected turns show no chips.
+3. `03_chip_filter_tests.md` — unit pins on the four observed live shapes + E2E chip-count assertions.
+
+## Testing & Quality
+- Unit: `tests/unit/test_retriever.py` (extend — the tiering table), `tests/unit/test_source_chip_quality.py` (new, task 03 — the four observed shapes), the done-frame schema tests (`related` defaults `[]`; old payloads without the field still parse).
+- E2E: `tests/e2e/test_source_chip_quality.py` (new, task 03; run in isolation: `uv run pytest tests/e2e/test_source_chip_quality.py -v --no-cov`) — a known single-source question → exactly one citation chip; a deflected question → zero `.source-chip` elements (the row, if any, is `.related-doc`, never `.source-chip`).
+- Regression: `tests/e2e/test_retrieval_quality.py`, `test_honest_deflection.py`, `test_chat_rag.py`, `test_sources_midstream_bug.py` stay green.
+- Coverage: **>90%** on `app/` (validate.sh gate).
+
+## Completion Criteria
+- [ ] For a single-document question, the turn shows one citation chip (E2E).
+- [ ] A weak 2nd doc renders only in the de-emphasized related row, never as a `.source-chip` (unit + E2E).
+- [ ] A deflected turn renders zero citation chips (the weak hits, if any, live in the related row).
+- [ ] `uv run pytest` green; coverage >90%; the e2e file green in isolation; `uv run ruff check . && uv run pyright` clean.
+- [ ] One `--no-gpg-sign` commit; phase dir moved to `complete/` by the pipeline gate.
+
+## Locked decisions
+- **A1 — direction: usefulness bar (server, deterministic) + visual split (UI); cite-gated chips rejected for now (owner-confirmed 2026-09-14, roadmap confirmation).**
+- **A2 — citation slot = vector-corroborated retrieval doc (best hit-chunk cosine >= `source_usefulness_floor`, default 0.35, env-tunable) OR agent-read doc; `top_n_docs` stays a ceiling, not a quota (owner-confirmed 2026-09-14).**
+- **A3 — `query_log.sources` keeps recording the full retrieval (observability); `done.sources` records only the cited tier (owner-confirmed 2026-09-14).**
+- **A4 — the related tier is capped at 2 docs (`related_max_docs`, env `BOR_RELATED_MAX_DOCS` — owner-confirmed 2026-09-14).**
+
+## Commit
+```bash
+git add app/ tests/ frontend/ .agents/phases/ && git commit --no-gpg-sign -m "feat(rag): tier sources by a usefulness bar — weak hits become a de-emphasized related-docs row, never citation chips"
+```