File size: 25,496 Bytes
2e818da
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
"""Hybrid, structure-aware retrieval over canonical academic evidence."""

from __future__ import annotations

import re
from collections import defaultdict
from dataclasses import dataclass
from typing import Sequence

from app.observability.operation import observe_operation, observe_stage
from app.observability.config import get_observability_config
from app.observability.sanitize import sanitize_attribute_value
from app.rag.evidence_store import EvidenceStore, LexicalCandidate
from app.rag.models import (
    ConsumerType,
    EvidenceCitation,
    EvidenceRequest,
    EvidenceType,
    RetrievedEvidence,
    RetrievalDiagnostics,
)
from app.rag.vector_indexes import PaperEvidenceIndex, VectorCandidate
from app.rag.project_memory import ProjectMemoryStore
from app.rag.reranker import EvidenceReranker
from app.rag.pipeline_version import CURRENT_PRODUCT_PIPELINE_VERSION


_RRF_K = 60
_STRUCTURAL_RELATIONS = {"caption_of", "describes", "parent", "continuation", "same_table"}
_SYNTHESIS_CONSUMERS = {
    ConsumerType.WIKI,
    ConsumerType.DRAFT,
    ConsumerType.REPORT,
    ConsumerType.PROJECT_GRAPH,
    ConsumerType.PAPER_GRAPH,
}
_VISUAL_TYPES = {
    EvidenceType.FIGURE,
    EvidenceType.PLOT,
    EvidenceType.DIAGRAM,
    EvidenceType.TABLE,
    EvidenceType.FORMULA,
    EvidenceType.CAPTION,
}
_REFERENCE_SECTION_RE = re.compile(r"^(references|bibliography|works cited)\b", re.IGNORECASE)


@dataclass(frozen=True)
class SourceRetrievalResult:
    evidence: list[RetrievedEvidence]
    citations: list[EvidenceCitation]
    diagnostics: RetrievalDiagnostics


class PaperEvidenceService:
    """The only product-facing source-evidence retrieval boundary."""

    def __init__(
        self,
        store: EvidenceStore | None = None,
        index: PaperEvidenceIndex | None = None,
        reranker: EvidenceReranker | None = None,
    ) -> None:
        self.store = store or EvidenceStore()
        self.index = index or PaperEvidenceIndex()
        self.reranker = reranker or EvidenceReranker()

    def retrieve(self, request: EvidenceRequest) -> SourceRetrievalResult:
        consumer = request.consumer.value
        diagnostics = RetrievalDiagnostics()
        with observe_operation(
            "rag.retrieve",
            subsystem="retrieval",
            consumer=consumer,
            attributes={
                "query_chars": len(request.query),
                "document_filter_count": len(request.document_ids),
                "anchor_request_count": len(request.anchor_evidence_ids) + len(request.selection_anchors),
                "token_budget": request.token_budget,
                "pipeline.version": CURRENT_PRODUCT_PIPELINE_VERSION,
            },
        ) as op:
            obs_config = get_observability_config()
            if obs_config.capture_content:
                op.event(
                    "local_diagnostic_query",
                    {"query_preview": sanitize_attribute_value(request.query[:240])},
                )
            with observe_stage(op, "anchor_resolution", subsystem="retrieval", consumer=consumer):
                anchor_ids = self._resolve_anchors(request)
            diagnostics.anchor_count = len(anchor_ids)

            lexical: list[LexicalCandidate] = []
            try:
                with observe_stage(op, "lexical_search", subsystem="retrieval", consumer=consumer):
                    lexical = self.store.lexical_search(
                        request.project_id,
                        request.query,
                        limit=40,
                        document_ids=request.document_ids or None,
                    )
            except Exception as exc:
                # SQLite/FTS is one independent retrieval channel. Preserve
                # dense/anchor recovery while making the handled degradation
                # visible on the parent request.
                op.record_exception(
                    exc,
                    escaped=False,
                    stage="lexical_search",
                    category="lexical_search_fallback",
                )
                diagnostics.terminal_state = "degraded"
                op.mark_terminal("degraded")
            diagnostics.lexical_candidate_count = len(lexical)

            dense: list[VectorCandidate] = []
            try:
                # This parent stage deliberately contains both the existing
                # embedding and Chroma child spans; do not add a duplicate
                # query-embedding operation here.
                with observe_stage(op, "dense_search", subsystem="retrieval", consumer=consumer):
                    dense = self.index.search(
                        request.project_id,
                        request.query,
                        limit=40,
                        document_ids=request.document_ids or None,
                        evidence_types=request.modalities or None,
                        consumer=consumer,
                    )
            except Exception as exc:  # lexical/anchor retrieval remains usable
                if not lexical and not anchor_ids:
                    raise
                diagnostics.warnings.append(f"dense_search_fallback:{type(exc).__name__}")
                op.record_exception(
                    exc,
                    escaped=False,
                    stage="dense_search",
                    category="dense_search_fallback",
                )
                diagnostics.terminal_state = "degraded"
                op.mark_terminal("degraded")
            diagnostics.dense_candidate_count = len(dense)

            with observe_stage(op, "rank_fusion", subsystem="retrieval", consumer=consumer):
                fused_ids, scores, reasons = _fuse(anchor_ids, lexical, dense)
            diagnostics.duplicates_removed = max(
                0,
                len(anchor_ids) + len(lexical) + len(dense) - len(fused_ids),
            )
            units = self.store.get_units(request.project_id, evidence_ids=fused_ids)
            unit_map = {unit.evidence_id: unit for unit in units}
            if request.modalities:
                unit_map = {
                    evidence_id: unit
                    for evidence_id, unit in unit_map.items()
                    if unit.element_type in request.modalities or evidence_id in anchor_ids
                }

            with observe_stage(op, "structural_expansion", subsystem="retrieval", consumer=consumer):
                expanded_ids = self._expand_structure(request.project_id, list(unit_map), limit=16)
                missing_ids = [evidence_id for evidence_id in expanded_ids if evidence_id not in unit_map]
                for unit in self.store.get_units(request.project_id, evidence_ids=missing_ids):
                    if request.document_ids and unit.document_id not in request.document_ids:
                        continue
                    unit_map[unit.evidence_id] = unit
                    scores[unit.evidence_id] = max(scores.get(unit.evidence_id, 0.0), 0.015)
                    reasons[unit.evidence_id].append("structural_neighbor")

            ranked = self._rank(request, unit_map, scores, reasons, anchor_ids, lexical, dense)
            with observe_stage(
                op, "reranking", subsystem="retrieval", consumer=consumer
            ) as rerank_stage:
                decision = self.reranker.decide(request, ranked)
                diagnostics.rerank_reason = decision.reason
                if decision.use:
                    try:
                        ranked = self.reranker.rerank(request.query, ranked)
                        diagnostics.rerank_used = True
                    except Exception as exc:  # local model failure must preserve fused retrieval
                        rerank_stage.mark_error(type(exc).__name__)
                        diagnostics.warnings.append(f"rerank_fallback:{type(exc).__name__}")
                        diagnostics.rerank_reason = "model_failure_fallback"
                        op.record_exception(
                            exc,
                            escaped=False,
                            stage="reranking",
                            category="rerank_fallback",
                        )
                        diagnostics.terminal_state = "degraded"
                        op.mark_terminal("degraded")

            with observe_stage(op, "diversity_selection", subsystem="retrieval", consumer=consumer):
                selected, truncated = _select_diverse(ranked, request)
            diagnostics.context_truncated = truncated
            diagnostics.fused_candidate_count = len(ranked)

            with observe_stage(op, "context_packing", subsystem="retrieval", consumer=consumer):
                diagnostics.documents_represented = len({item.evidence.document_id for item in selected})
                diagnostics.sections_represented = len(
                    {(item.evidence.document_id, tuple(item.evidence.section_path)) for item in selected}
                )
                diagnostics.source_context_chars = sum(len(item.evidence.index_text) for item in selected)
            if not selected and diagnostics.terminal_state == "success":
                diagnostics.terminal_state = "success_empty"
                op.mark_terminal("success_empty")

            op.add_count("query_chars", len(request.query))
            op.add_count("anchor_count", diagnostics.anchor_count)
            op.add_count("lexical_candidate_count", diagnostics.lexical_candidate_count)
            op.add_count("dense_candidate_count", diagnostics.dense_candidate_count)
            op.add_count("fused_candidate_count", diagnostics.fused_candidate_count)
            op.add_count("returned_evidence_count", len(selected))
            op.add_count("duplicates_removed", diagnostics.duplicates_removed)
            op.add_count("documents_represented", diagnostics.documents_represented)
            op.add_count("sections_represented", diagnostics.sections_represented)
            op.add_count("context_token_budget", request.token_budget)
            op.add_count("context_truncated", int(diagnostics.context_truncated))
            op.add_count("source_context_chars", diagnostics.source_context_chars)
            op.add_count("empty_result", int(not selected))
            op.set("rerank_used", diagnostics.rerank_used)
            op.set("rerank_reason", diagnostics.rerank_reason)
            for evidence_type in EvidenceType:
                count = sum(1 for item in selected if item.evidence.element_type is evidence_type)
                if count:
                    op.add_count(f"returned_type.{evidence_type.value}", count)
            with observe_stage(op, "citation_materialization", subsystem="retrieval", consumer=consumer):
                citations = self._citations(request.project_id, selected)
            diagnostics.stage_ms = op.stage_durations_ms
            return SourceRetrievalResult(evidence=selected, citations=citations, diagnostics=diagnostics)

    def ground_graph_nodes(
        self,
        project_id: str,
        requests: Sequence[tuple[str, str, Sequence[str]]],
    ) -> tuple[dict[str, list[str]], dict[str, list[str]]]:
        """Ground a graph in one evidence read and one memory read.

        Graph construction can contain 25 nodes. It must not issue 25 FTS
        queries plus selective embedding calls on the request path.
        """

        with observe_operation(
            "rag.ground_graph_nodes",
            subsystem="retrieval",
            consumer="project_graph",
            attributes={"node_request_count": len(requests)},
        ) as op:
            units = self.store.get_units(project_id)
            memories = ProjectMemoryStore(self.index.db).list_project(project_id)
            evidence_result: dict[str, list[str]] = {}
            memory_result: dict[str, list[str]] = {}
            for node_id, query, document_ids in requests:
                allowed = set(document_ids)
                ranked_units = sorted(
                    (
                        (_term_overlap(query, unit.index_text), unit.ordinal, unit.evidence_id)
                        for unit in units
                        if unit.index_text.strip() and (not allowed or unit.document_id in allowed)
                    ),
                    key=lambda item: (-item[0], item[1]),
                )
                evidence_result[node_id] = [
                    evidence_id for score, _, evidence_id in ranked_units if score > 0
                ][:4]
                ranked_memories = sorted(
                    ((_term_overlap(query, item.statement), item.memory_id) for item in memories),
                    key=lambda item: (-item[0], item[1]),
                )
                memory_result[node_id] = [
                    memory_id for score, memory_id in ranked_memories if score > 0
                ][:2]
            op.add_count("source_evidence_count", sum(map(len, evidence_result.values())))
            op.add_count("project_memory_count", sum(map(len, memory_result.values())))
            if not evidence_result:
                op.mark_terminal("success_empty")
            return evidence_result, memory_result

    def project_outlines(self, project_id: str) -> list[dict[str, object]]:
        """Return canonical structural evidence for initial graph generation."""

        with observe_operation(
            "rag.project_outlines",
            subsystem="retrieval",
            consumer="project_graph",
        ) as op:
            outlines: list[dict[str, object]] = []
            structural_types = {
                EvidenceType.TITLE,
                EvidenceType.HEADING,
                EvidenceType.SECTION_CARD,
                EvidenceType.TABLE,
                EvidenceType.FIGURE,
                EvidenceType.PLOT,
                EvidenceType.DIAGRAM,
            }
            for document in self.store.list_documents(project_id):
                units = [
                    unit
                    for unit in self.store.get_units(
                        project_id,
                        document_ids=[document.document_id],
                    )
                    if unit.element_type in structural_types
                ][:80]
                outlines.append({
                    "filename": document.filename,
                    "document_id": document.document_id,
                    "structure": "\n\n".join(
                        f"[{unit.evidence_id} | page {unit.page_start} | {unit.element_type.value}]\n{unit.index_text}"
                        for unit in units
                    )[:16000],
                    "evidence_ids": [unit.evidence_id for unit in units],
                })
            op.add_count("documents_represented", len(outlines))
            op.add_count(
                "source_evidence_count",
                sum(len(item["evidence_ids"]) for item in outlines),
            )
            if not outlines:
                op.mark_terminal("success_empty")
            return outlines

    def project_citation_material(self, project_id: str) -> list[dict[str, object]]:
        """Return front matter and bibliography from canonical evidence only."""

        with observe_operation(
            "rag.project_citation_material",
            subsystem="retrieval",
            consumer="paper_graph",
        ) as op:
            payloads: list[dict[str, object]] = []
            for document in self.store.list_documents(project_id):
                units = self.store.get_units(
                    project_id,
                    document_ids=[document.document_id],
                )
                front_units = [
                    unit for unit in units
                    if unit.page_start == 1
                    and unit.element_type in {
                        EvidenceType.TITLE,
                        EvidenceType.HEADING,
                        EvidenceType.PARAGRAPH,
                    }
                ][:20]
                reference_units = [
                    unit for unit in units
                    if (
                        unit.element_type is EvidenceType.REFERENCE
                        or self._is_reference_section_unit(unit.section_path)
                    )
                    and unit.index_text.strip()
                ]
                reference_units.sort(key=lambda unit: unit.ordinal)
                references = [
                    unit.raw_text.strip() or unit.index_text
                    for unit in reference_units
                ]
                # ``index_text`` includes an internal retrieval envelope
                # (Paper/Section/Element labels).  Citation identity must use
                # the source text, never that implementation detail.
                front_text = "\n".join(
                    unit.raw_text.strip() or unit.index_text
                    for unit in front_units
                )
                body = "\n".join(
                    part for part in (
                        document.title,
                        document.abstract,
                        front_text,
                        "References\n" + "\n".join(references) if references else "",
                    ) if part
                )
                payloads.append({
                    "file_id": document.document_id,
                    "filename": document.filename,
                    "text": body,
                    "document_metadata": {
                        "Title": document.title,
                        "Author": "; ".join(document.authors),
                    },
                    "front_matter_text": front_text,
                    "reference_evidence_ids": [
                        unit.evidence_id for unit in reference_units
                    ],
                })
            op.add_count("documents_represented", len(payloads))
            op.add_count(
                "source_evidence_count",
                sum(len(item["reference_evidence_ids"]) for item in payloads),
            )
            if not payloads:
                op.mark_terminal("success_empty")
            return payloads

    @staticmethod
    def _is_reference_section_unit(section_path: Sequence[str]) -> bool:
        """Support evidence written before bibliography headings were normalized."""

        if not section_path:
            return False
        heading = re.sub(r"[*_`]+", "", section_path[-1] or "").strip()
        return bool(_REFERENCE_SECTION_RE.match(heading))

    def _resolve_anchors(self, request: EvidenceRequest) -> list[str]:
        ids = list(request.anchor_evidence_ids)
        for anchor in request.selection_anchors:
            if anchor.evidence_id:
                ids.append(anchor.evidence_id)
            if anchor.region_id:
                ids.extend(
                    self.store.resolve_region(
                        request.project_id,
                        anchor.document_id,
                        anchor.region_id,
                    )
                )
            ids.extend(
                self.store.resolve_selection(
                    request.project_id,
                    anchor.document_id,
                    anchor.page_number,
                    anchor.boxes,
                    anchor.text,
                )
            )
        existing = self.store.get_units(request.project_id, evidence_ids=list(dict.fromkeys(ids)))
        allowed_documents = set(request.document_ids)
        return [
            unit.evidence_id
            for unit in existing
            if not allowed_documents or unit.document_id in allowed_documents
        ]

    def _expand_structure(self, project_id: str, evidence_ids: Sequence[str], limit: int) -> list[str]:
        relations = self.store.get_relations(evidence_ids)
        expanded: list[str] = []
        for relation in relations:
            if str(relation.relation_type) not in _STRUCTURAL_RELATIONS:
                continue
            if relation.source_evidence_id in evidence_ids:
                expanded.append(relation.target_evidence_id)
            if relation.target_evidence_id in evidence_ids:
                expanded.append(relation.source_evidence_id)
        return list(dict.fromkeys(expanded))[:limit]

    def _rank(
        self,
        request: EvidenceRequest,
        units: dict,
        fused_scores: dict[str, float],
        reasons: dict[str, list[str]],
        anchor_ids: Sequence[str],
        lexical: Sequence[LexicalCandidate],
        dense: Sequence[VectorCandidate],
    ) -> list[RetrievedEvidence]:
        lexical_scores = {candidate.evidence_id: candidate.score for candidate in lexical}
        dense_scores = {candidate.item_id: candidate.score for candidate in dense}
        anchors = set(anchor_ids)
        ranked: list[RetrievedEvidence] = []
        for evidence_id, unit in units.items():
            structural = 0.0
            if evidence_id in anchors:
                structural += 1.0
            if unit.element_type in {EvidenceType.SECTION_CARD, EvidenceType.LOCAL_WINDOW}:
                structural += 0.05 if request.consumer in _SYNTHESIS_CONSUMERS else -0.01
            if unit.element_type in _VISUAL_TYPES and request.consumer in {
                ConsumerType.VISUALIZATION,
                ConsumerType.CHAT,
                ConsumerType.WIKI,
            }:
                structural += 0.04
            if unit.quality_flags:
                structural -= 0.01 * min(3, len(unit.quality_flags))
            ranked.append(
                RetrievedEvidence(
                    evidence=unit,
                    fused_score=fused_scores.get(evidence_id, 0.0) + structural,
                    dense_score=dense_scores.get(evidence_id),
                    lexical_score=lexical_scores.get(evidence_id),
                    structural_score=structural,
                    retrieval_reasons=list(dict.fromkeys(reasons.get(evidence_id, []))),
                )
            )
        ranked.sort(key=lambda item: (-item.fused_score, item.evidence.ordinal))
        return ranked

    def _citations(
        self,
        project_id: str,
        evidence: Sequence[RetrievedEvidence],
    ) -> list[EvidenceCitation]:
        documents = {doc.document_id: doc for doc in self.store.list_documents(project_id)}
        return [
            EvidenceCitation(
                evidence_id=item.evidence.evidence_id,
                document_id=item.evidence.document_id,
                filename=documents.get(item.evidence.document_id).filename
                if item.evidence.document_id in documents
                else "",
                page_start=item.evidence.page_start,
                page_end=item.evidence.page_end,
                bbox_norm=item.evidence.bbox_norm,
                section_path=item.evidence.section_path,
            )
            for item in evidence
        ]


def _fuse(
    anchor_ids: Sequence[str],
    lexical: Sequence[LexicalCandidate],
    dense: Sequence[VectorCandidate],
) -> tuple[list[str], dict[str, float], dict[str, list[str]]]:
    scores: dict[str, float] = defaultdict(float)
    reasons: dict[str, list[str]] = defaultdict(list)
    order: list[str] = []
    for anchor_rank, evidence_id in enumerate(anchor_ids):
        scores[evidence_id] += max(1.25, 2.0 - anchor_rank * 0.08)
        reasons[evidence_id].append("explicit_anchor")
        order.append(evidence_id)
    for rank, candidate in enumerate(lexical, 1):
        scores[candidate.evidence_id] += 1.0 / (_RRF_K + rank)
        reasons[candidate.evidence_id].append("lexical")
        order.append(candidate.evidence_id)
    for rank, candidate in enumerate(dense, 1):
        scores[candidate.item_id] += 1.0 / (_RRF_K + rank)
        reasons[candidate.item_id].append("dense")
        order.append(candidate.item_id)
    return list(dict.fromkeys(order)), scores, reasons


def _term_overlap(query: str, text: str) -> int:
    terms = {
        term
        for term in re.findall(r"[a-zA-Z][a-zA-Z0-9_-]{2,}", query.casefold())
        if term not in {"about", "from", "paper", "that", "this", "with"}
    }
    lowered = text.casefold()
    return sum(1 for term in terms if term in lowered)


def _select_diverse(
    ranked: Sequence[RetrievedEvidence],
    request: EvidenceRequest,
) -> tuple[list[RetrievedEvidence], bool]:
    char_budget = max(1024, request.token_budget * 4)
    per_document = 8 if request.consumer in _SYNTHESIS_CONSUMERS else 5
    per_section = 3
    selected: list[RetrievedEvidence] = []
    document_counts: dict[str, int] = defaultdict(int)
    section_counts: dict[tuple[str, tuple[str, ...]], int] = defaultdict(int)
    used_chars = 0
    truncated = False
    for item in ranked:
        unit = item.evidence
        section_key = (unit.document_id, tuple(unit.section_path))
        anchored = "explicit_anchor" in item.retrieval_reasons
        if not anchored and (
            document_counts[unit.document_id] >= per_document or section_counts[section_key] >= per_section
        ):
            continue
        size = max(1, len(unit.index_text))
        if selected and used_chars + size > char_budget:
            truncated = True
            continue
        selected.append(item)
        document_counts[unit.document_id] += 1
        section_counts[section_key] += 1
        used_chars += size
    return selected, truncated