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docs(scm): document real size-changing PAC reintegration
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‎docs/research/dmc3-scm-real-size-changing-pac-reintegration-2026-09-13.md‎

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# DMC3 SCM — real size-changing canonical rebuild and parent PAC reintegration
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Date: 2026-09-13
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Project: DMC Rengine
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Branch: `reverse/mod-completion-20260907`
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PR: #386
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Evidence class: `REAL_CORPUS_BOUND_SCM_SIZE_CHANGING_CANONICAL_REBUILD_AND_PARENT_PAC_REINTEGRATION`
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## Purpose
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Close the explicit SCM writer/integration blocker that remained after the preserve-layout alpha/translation/rotation receipts:
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```text
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hash-bound real SCM payload
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-> typed size-changing structural edit
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-> preserve-layout rejection
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-> deterministic canonical_rebuild
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-> canonical SCM reparse
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-> real parent PAC packed reflow
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-> staged reopen
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-> exact authored-child rematerialization
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-> exact preservation of every non-target physical slot
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```
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This proves a bounded real-retail size-changing SCM reflow path. It does **not** prove NBZ delivery or original `dmc3.exe` acceptance.
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## Source authority
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Real hash-bound child:
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```text
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resource st001.scm
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size 887,760 bytes
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SHA-256 3ed787cc8a41f4c21b972664cf4174739382230ce0010f166c32c2a9e3626ba5
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parent slot PAC physical slot 2
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slot offset 3,485,792 / 0x353060
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```
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Real parent:
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```text
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resource st001.pac
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size 4,632,960 bytes
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SHA-256 43034a2e0596f744ea2d50fd785b2783d319fe5f0c7e15061e7c68b2786a57d9
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format PAC
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slots 8
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```
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The child and parent are hash-bound real corpus evidence. The parent is not promoted to protected-install/original-resolver-selected provenance.
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## Exact CI-built runner
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The acceptance run used the Ubuntu artifact from PR #386 exact branch head:
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```text
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branch head SHA 08d9c7935316d9afa2991e3210a02561099a9011
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workflow run 34759963639
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Ubuntu Build + full CTest PASS
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Windows Build + full CTest PASS
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artifact id 10318353331
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artifact name dmc-rengine-linux-fcc9df0cd25addcc288c2f0ed36f59d37fba1b06
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artifact digest sha256:77b106594215287e9d7514910b016c1094288b944cd2d9d709dcf3d8c5d97c02
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executable SHA e22f7ee8cf31e26758c207658e20416abcfdbef6b83ea15681c5e920b2997a86
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```
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The artifact filename is workflow-generated and carries the PR merge-ref SHA label; the artifact metadata separately binds it to branch head `08d9c793...`.
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## Controlled size-changing edit
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Command class: `scm-append-break-vertex-copy` / typed API `append_break_vertex_copy()`.
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Selected target:
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```text
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object 0
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mesh 0
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source vertex 166
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source mesh count 167
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output mesh count 168
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```
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The authoring operation copies one existing vertex across position/normal/UV/RGB data and appends the confirmed topology break bit `0x02`. This grows the serialized stream count while deliberately not creating an additional non-degenerate triangle.
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Exact observed result:
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```text
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SCM_SIZE_CHANGING_REBUILD_OK
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sourceVertices=167
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outputVertices=168
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sourceObjectVertices=167
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outputObjectVertices=168
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sourceSize=887760
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outputSize=887776
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sizeDelta=16
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trianglesBefore=118
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trianglesAfter=118
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appendedTopology=2
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reparse=PASS
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publication=NO_REPLACE_PASS
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```
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`preserve_layout` rejected the stream-count change as required. `canonical_rebuild` succeeded and produced:
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```text
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size 887,776 bytes
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SHA-256 467734f48d96c76eb44abb395280a8743fac0ce959dbd26c5ce226f928cb9cc2
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```
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A second independent run with the same exact CI binary produced byte-identical authored SCM output.
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## Real parent PAC packed reflow
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The authored SCM was passed to the provenance-bound `verify-scm-reintegration` path against physical slot 2 of the source parent.
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Observed result:
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```text
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SCM_REINTEGRATION_VERIFIED
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format=PAC
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slot=2
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targetAliases=1
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sourceScmBytes=887760
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authoredScmBytes=887776
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sourceParentBytes=4632960
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outputParentBytes=4632976
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targetAliasRematerialization=PASS
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nonTargetPhysicalSpansExact=PASS
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authoredScmReparse=PASS
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publication=NO_REPLACE_PASS
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```
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Rebuilt parent:
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```text
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size 4,632,976 bytes
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size delta +16
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SHA-256 adb978f58926f0f04cd2d72fe3fc12a410d9dd9c2277819f9637cb71d4b9c5f6
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```
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A repeated run produced the same parent bytes and SHA-256.
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## Independent slot-preservation check
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After rebuilding, the output PAC was reopened independently and every top-level physical slot was extracted and hashed.
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| Slot | Source offset | Output offset | Size | SHA-256 / result |
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| ---: | ---: | ---: | ---: | --- |
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| 0 | 48 | 48 | 48 | `7efcf182f28135a3d694324ba06715ca6f6b075a028d035c89c69809df23faa5` — exact |
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| 1 | 96 | 96 | 3,485,696 | `976e6a6961686572c66cb6935f7e44dd450990016071604d99ff831ed9d36d5a` — exact |
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| 2 | 3,485,792 | 3,485,792 | 887,760 -> 887,776 | source `3ed787...` -> authored `467734...` |
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| 3 | 4,373,552 | 4,373,568 | 26,160 | `80b4b64318d84748c34a9e4f08065e35998e2e14e3766affb653e0f26adab77a` — exact |
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| 4 | 4,399,712 | 4,399,728 | 256 | `36d40827c90e7ce0750a56c0f267be6721dd2b2e4bf30f4100a0cd6ecdabc07e` — exact |
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| 5 | 4,399,968 | 4,399,984 | 167,888 | `500dadbc8e0db8d8d232fa04c49db437d41cbe6c50e555e24d91e758c6bcc4b0` — exact |
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| 6 | 4,567,856 | 4,567,872 | 1,648 | `0f3d9952b61e3d1346dc9910c9c401fc0214d0d6fb2593791e0c000cc4599f64` — exact |
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| 7 | 4,569,504 | 4,569,520 | 63,456 | `f0c0a2252f26d8e6f1538bc307b9c2ebf9a785e5d11b1fbe4ffc45672a3a5487` — exact |
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All seven non-target top-level slots are byte-identical. Slots after the changed SCM shift by exactly `+16` bytes, matching the child growth. The nested PNST in slot 5 and nested PAC in slot 7 still expand through the canonical container path.
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## Independent authored-child rematerialization
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Physical slot 2 was re-extracted from the rebuilt parent after reopen:
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```text
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size 887,776 bytes
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SHA-256 467734f48d96c76eb44abb395280a8743fac0ce959dbd26c5ce226f928cb9cc2
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```
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It is byte-identical to the authored SCM emitted before reintegration, and canonical SCM parse succeeds.
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## Promotion result
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The previous blocker **`real-retail size-changing canonical rebuild` is closed for this explicit bounded class**.
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The evidence now supports:
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- a typed size-changing SCM edit on a hash-bound real payload;
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- mandatory preserve-layout rejection for that stream-count change;
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- deterministic canonical layout reflow;
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- canonical reparse of the larger SCM;
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- real parent PAC packed reflow;
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- exact authored-child rematerialization after parent reopen;
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- byte-exact preservation of every non-target top-level physical slot.
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## Evidence boundary
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Still open and not promoted by this receipt:
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- provenance-bound retail texture rewrite;
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- broader PNST authored-delivery coverage for SCM;
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- retail NBZ authored-resource delivery;
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- original resolver selection of the authored overlay;
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- original `dmc3.exe` acceptance and consumer-visible effect;
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- universal/100% production SCM writer authority;
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- Capcom offline-builder equivalence.
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Machine receipt: `data/reverse/dmc3-scm-real-size-changing-pac-reintegration-attestation-20260913.json`.
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No proprietary SCM or PAC payload bytes are committed.

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