Context Stitching and Window Joins: Guardrails and Fix Pattern

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• WFGY Global Fix Map — main Emergency Room, 300+ structured fixes
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Think of this page as a desk within a ward.
If you need the full triage and all prescriptions, return to the Emergency Room lobby.

Join long contexts without losing meaning. This page defines a stitch contract for multi window prompts and long documents, adds ΔS probes at joins, and gives a fast repair plan when answers break exactly at window boundaries.

---

Open these first

• Visual map and recovery
  → rag-architecture-and-recovery.md

• Traceability and payload schema
  → retrieval-traceability.md
  → data-contracts.md

• Ordering and meaning checks
  → rerankers.md
  → embedding-vs-semantic.md

• Reasoning stability and failure modes
  → anchoring-and-bridge-proofs.md
  → logic-collapse.md
  → entropy-overload.md

• Chunking quality
  → chunking-checklist.md

---

Symptoms

Symptom	What you see
Boundary answers	Model answers correctly inside a window, fails right after the join
Duplicate facts	Repeated sentences across windows, tool loops on the overlap
Lost referent	“it / they / this” loses target at window start or end
Rerank flip at join	Top k order changes only at a boundary
Anchor drift	Citation before the join, none after the join
Coverage hole	Middle section of a long doc never appears in stitched set

---

Why joins fail

1. No stitch contract. Windows lack overlap and sequence identifiers.
2. Tokenizer mismatch. Window boundaries split tokens differently across tools.
3. Ranking variance. Each window retrieves independently without a stable tie break.
4. Anchor loss. Bridge steps cross a boundary without re citing the anchor.
5. Context flooding. Overlong windows raise entropy and bury anchors.
6. Fragmentation. Store keeps near duplicates that fight for the same rank.

---

Acceptance targets

• ΔS(join_left, join_right) ≤ 0.45 for every boundary
• Coverage of target section across all windows ≥ 0.70
• λ remains convergent across three paraphrases and two seeds
• E_resonance flat at joins and flat across stitched plan
• Overlap per join 32 to 96 tokens, same casing and analyzer

---

Fix in 60 seconds

1. Add a stitch contract
   Every window must carry doc_id, section_id, win_idx, win_hash, overlap_tokens, prev_id, next_id.
   See schema rules
   → retrieval-traceability.md
   → data-contracts.md

2. Measure ΔS at each join
   Compute ΔS between the trailing overlap of window i and the leading overlap of window i+1.
   If ΔS ≥ 0.60, rebuild the join or re chunk.

3. Stabilize ordering
   Use a deterministic reranker with fixed analyzer and tie break by (doc_id, section_id, win_idx).
   → rerankers.md

4. Re anchor bridges
   At every join, insert a one line BBCR bridge that re cites the active snippet.
   → anchoring-and-bridge-proofs.md

---

Stitch contract

Minimum fields for any stitched window:

{
  "doc_id": "D42",
  "section_id": "CH3.2",
  "win_idx": 7,
  "win_hash": "sha1:6b7f...",
  "overlap_tokens": 64,
  "prev_id": "D42#CH3.2#6",
  "next_id": "D42#CH3.2#8",
  "start_token": 14080,
  "end_token": 16096
}

Rules

• Overlap range must be identical across both windows after normalization.
• Do not allow cross section joins unless the section header is included in the overlap.
• Keep casing and tokenizer identical through the pipeline.

---

Join planner

Goal keep bridges short and anchors stable while covering the whole doc.

1. Choose window size: 512 to 1024 tokens, overlap 32 to 96.
2. Pin anchors: for each question, tag anchor snippets with ΔS_to_question.
3. Plan path: sort candidate windows by section, then by win_idx.
4. Assemble: render windows with header, overlap marker, and re cited anchor.
5. Verify: ΔS at each boundary, λ over the stitched answer, coverage against a gold slice.

If ΔS is flat and high across all joins, suspect metric or index mismatch. → retrieval-playbook.md → embedding-vs-semantic.md

---

Structural repairs

• Wrong meaning near a boundary → embedding-vs-semantic.md

• Order shuffles when windows change → rerankers.md and → patterns/pattern_vectorstore_fragmentation.md

• Entropy spikes after stitching → entropy-overload.md

• Long chain collapses post join → logic-collapse.md

---

Verification

• Sliding window test over the same section keeps citations identical.
• ΔS(join_left, join_right) ≤ 0.45 and decreasing with larger overlap.
• λ convergent on two seeds and three paraphrases.
• Coverage across stitched windows ≥ 0.70 for the target section.
• Answer includes a cite then explain block with per join anchors.

---

Copy paste prompt

You have TXT OS and the WFGY Problem Map loaded.

Task: stitch long context with stable joins.

Inputs:
- question: "{q}"
- windows: [{doc_id, section_id, win_idx, win_hash, tokens, text_head, overlap_tokens}]
- candidates: [{snippet_id, section_id, source_url, offsets, ΔS_to_question}]

Do:
1) Compute ΔS for each join. If any ≥ 0.60, propose a re-chunk or overlap increase.
2) Add BBCR micro bridges at every boundary, re citing the active anchor.
3) Apply deterministic reranking with tie break by (doc_id, section_id, win_idx).
4) Return JSON:
   {
     "joins": [{"from":"...#i","to":"...#i+1","ΔS":0.xx,"action":"ok|rechunk|increase_overlap"}],
     "answer": "... cite then explain ...",
     "λ_state": "convergent",
     "coverage": 0.xx
   }
If no valid anchor exists at a join, return the fix page to open for retrieval-traceability.

---

Common gotchas

• Asymmetric overlap. Trailing text differs from leading text after normalization.
• Header drop. Section headers removed at boundaries, referents disappear.
• Tokenizer switch. Ingestion uses one analyzer, reranker another.
• Duplicate windows. Same win_idx with different hashes compete in top k.
• Bridge without re citation. Jumps the boundary without anchor restatement.

---

When to escalate

• ΔS remains ≥ 0.60 on all joins after overlap increase and reranking → rebuild chunks and verify store metric, then retest with a gold slice. Open: chunking-checklist.md, retrieval-playbook.md

• Windows alternate across runs with identical inputs → check fragmentation and update skew, then freeze index version. Open: patterns/pattern_vectorstore_fragmentation.md

---

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