# P3-S25.1D — MULTI-CHUNK TURN SEMANTIC INVARIANCE

> **Document type** : Governance / evidence (P3-S25.1D)
> **Date**           : 2026-08-28
> **Scope**          : VERIFICATION ONLY. No real-source ingestion.

## Question

`batching != semantic transformation`. Grouping several already-validated
24 MiB atomic chunks into a single multi-chunk turn must not change the final
semantic output of the tick -> M15/M30 aggregation:

```
single-stream reference == batch 1 == batch 2 == batch 4 == batch 6
```

The turn boundary must have ZERO semantic significance.

## Semantic contract compared

`rows_processed`, `m15_count`, `m30_count`, `m15_hash`, `m30_hash`,
`output_hash`, `output_carry_m15`, `output_carry_m30`, `final_state_hash`.

## Method

On a fresh-allocated disposable range — bytes `[0, 150,994,944)` = 6 full
24 MiB atomic chunks, wholly within the committed chunks 0..10 region (which
ends at byte 163,578,081) and before real chunk 11 — the same hardened
driver runs:

- single-stream reference : the whole range as one stream;
- batch 1 / 2 / 4 / 6      : each turn processes a bounded batch of atomic
  chunks, one disposable checkpoint after EVERY atomic chunk, then proceeds.

All configurations start from the same initial empty carry and use identical
parser, aggregator, canonical ordering, canonical serialization, and SHA-256
hashing. Byte-contiguity is enforced at the actual line-safe consumed offset
(`pos += len(raw)`), as in production.

## Exact result (machine-readable)

Authoritative evidence:
`ml/p3/p3_s251_external_ingest/multichunk_benchmark/output/multichunk_invariance.json`
-> `semantic_invariant = true` (classification PASS).

| config | rows_processed | m15_count | m30_count | final_state_hash |
|--------|---------------:|----------:|----------:|------------------|
| reference | 3,379,465 | 17,374 | 9,315 | cb1e7d17d6.. |
| batch 1 | 3,379,465 | 17,374 | 9,315 | cb1e7d17d6.. |
| batch 2 | 3,379,465 | 17,374 | 9,315 | cb1e7d17d6.. |
| batch 4 | 3,379,465 | 17,374 | 9,315 | cb1e7d17d6.. |
| batch 6 | 3,379,465 | 17,374 | 9,315 | cb1e7d17d6.. |

Conclusion: **CHUNK-BATCH SEMANTIC INVARIANCE — PASS**. Grouping chunks into
turns is an execution detail, never a semantic transformation.

## Boundary-continuity requirement (recorded & resolved)

Chunking at nominal fixed byte multiples is unsafe: a tick record can straddle
the chunk boundary. Each chunk must be read line-safely and the next chunk
must start at the actual consumed end of the previous one. After that driver
correction, the batched row count exactly equals the reference with identical
hashes. See `P3_S25_1D_VERIFICATION_DRIVER_HARDENING.md`.