diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 06fad6b..a89adb0 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -144,10 +144,18 @@ not repeat the matrix; source updates and reopen events run it again. Native CI
 uses pinned `cargo-nextest` for unit and
 integration tests, followed by `cargo test --doc` with the same workspace features;
 the production feature graph and release workspace are still checked separately.
-PRs restore Cargo caches without uploading merge-ref snapshots. The default branch
+Native-test PR jobs restore Cargo caches without uploading merge-ref snapshots. The default branch
 publishes reusable snapshots per dependency/toolchain configuration; a cache hit
 never skips current-commit tests. Downloads are shared between architectures of
 the same OS, while compiled targets remain isolated by architecture and SDK.
+
+Auxiliary UI screenshots must not add a second automatic upstream PR build matrix.
+Keep contributor-owned screenshot builds and publication in the source fork;
+upstream capture needs an explicitly requested run and read-only target-cache
+restoration. Screenshot evidence must identify its source commit and does not
+replace native regression tests. The registered upstream screenshot workflow is
+disabled as recorded in the [cache ownership decision](architecture/notes/scripts/ci/2026-09-28-upstream-screenshot-cache-ownership.md).
+
 Local hooks are convenient, but bypassable; they are not the enforcement boundary.
 Submitting a workflow or `CODEOWNERS` file does not configure server-side rules.
 
@@ -162,6 +170,7 @@ feature work; there is no routine `--skip-architecture` option.
 - 先读架构图、工程合同和决策记录；按职责拆分，不按行号切片。
 - 一个 PR 只做一件事；改动超过 1500 行源码（不计文档、lockfile、资源）`pr-size` 会失败，请拆分。
 - Draft 和 Ready PR 都先运行必需的格式检查和矩阵规划，再执行五平台原生测试及两项 macOS release 编译检查；每个 Mac 在同一 runner 完成两类检查，原有 release 检查名称由轻量结果汇总保留。十项必需检查全绿才能合并，不省略平台或 doctest。
+- 附加截图留在贡献者 fork 中生成；上游按需执行，不重复自动跑整套截图构建，也不上传 PR 专属的大型编译缓存。截图与原生回归测试不能互相替代。
 - 2000 行是现有仓库的防灾上限，800 行只提示审查，不是“大厂标准”。
 - 普通功能 PR 不得增加存量债务；有问题的规则可以修订，但要有反例、测试和维护者审批。
 - 新增核心抽象、依赖方向、持久化或线程模型改变要先说明设计，不强迫每个小修复写 ADR。
diff --git a/architecture/notes/scripts/ci/2026-09-28-upstream-screenshot-cache-ownership.md b/architecture/notes/scripts/ci/2026-09-28-upstream-screenshot-cache-ownership.md
new file mode 100644
index 0000000..a0bd53c
--- /dev/null
+++ b/architecture/notes/scripts/ci/2026-09-28-upstream-screenshot-cache-ownership.md
@@ -0,0 +1,110 @@
+# Keep auxiliary screenshot work from displacing shared native caches
+
+## Status
+
+Operational change applied and read back on 2026-09-28. This note records the
+upstream workflow registration and cache cleanup; committing documentation alone
+does not change GitHub settings. No branch-protection rule was changed.
+
+## Context
+
+The required native suite publishes reusable default-branch snapshots and restores
+them read-only on PRs. An auxiliary screenshot workflow introduced through open
+fork PRs independently built complete Windows/macOS release applications and
+published large PR-scoped Rust caches in the upstream repository.
+
+The screenshot workflow is absent from `main` at `8087306b`, but its GitHub
+registration still accepted events for PR branches that supplied the file. Editing
+only a workflow on `main` would not change those already-open fork branches.
+
+## Evidence
+
+- [Native run 36327240193](https://github.com/Kuddev/pebrel/actions/runs/36327240193)
+  took 85m29s. Its Intel Mac queued for 48m07s and executed for 36m47s. Both Mac
+  architectures missed their native and release target caches, with the same
+  keys used by previously available default-branch entries.
+- The cache inventory contained four `v0-rust-native-ui-` snapshots scoped to
+  PR merge refs, together using 5.39 GB. The previously observed default-branch
+  Mac target snapshots were no longer present. These observations establish
+  cache pressure and misses, not an audit of who deleted each older entry.
+- [Screenshot run 36325527329](https://github.com/Kuddev/pebrel/actions/runs/36325527329)
+  used `.github/workflows/ui-review-screenshots.yml` from a fork PR. Its source
+  ran on both fork pushes and upstream PR updates; its publication job was
+  explicitly restricted to the source fork's push events. Upstream repeated the
+  full application builds but did not run that publication job.
+- The screenshot action used `Swatinem/rust-cache` with failure caching and no
+  read-only restriction. GitHub's [cache scope rules](https://docs.github.com/en/actions/reference/workflows-and-actions/dependency-caching)
+  do not make one PR's merge-ref cache available to sibling PRs merely because
+  their visible cache keys match.
+
+## Decision
+
+- Disable only the upstream `UI review screenshots` registration, workflow ID
+  `366570225`, through the documented workflow API. Leave source-fork workflow
+  `366585525` active. No contributor branch or application code is rewritten.
+- Preserve the full five-platform native suite, release-profile checks, required
+  contexts, assertions, feature graphs, packaging and branch-protection rules.
+  Auxiliary screenshot evidence remains separate from native regression coverage.
+- After confirming there are no active screenshot runs, remove only identified
+  upstream PR-scoped `v0-rust-native-ui-` entries. Preserve every default-branch
+  cache, release artifact and source file. Do not install recurring broad cleanup.
+- Keep contributor screenshot publication in its source repository. Any future
+  upstream screenshot entrypoint must be explicitly requested, restore target
+  caches read-only, and retain exact-source evidence before it is enabled.
+
+## Rejected alternatives
+
+- Delete all caches: would force more cold native and release checks.
+- Raise storage quota or buy runners first: does not address duplicate upstream
+  builds or the unshared snapshots that caused the observed competition.
+- Push fixes into all contributor branches immediately: creates new PR heads and
+  repeats their required native matrices. The upstream registration can be stopped
+  without editing their feature code or interrupting their fork publication.
+- Add a new scanning framework or equivalent CI gate: unnecessary for retiring
+  this identified auxiliary registration. A source check alone also does not stop
+  an already-running workflow from publishing another snapshot.
+- Remove native platforms, Markdown regressions or assertions: changes required
+  coverage rather than addressing resource ownership.
+
+## Consequences
+
+Upstream PR updates no longer launch this registered screenshot workflow. Native
+tests still run normally, including for docs-only changes. Source-fork screenshot
+builds and artifacts remain available for review with their source identity.
+
+At cleanup time only one of the identified PR screenshot entries remained. Removing
+it freed 1,351,294,893 bytes; the other previously observed entries were already
+absent and are not counted as deletions performed by this change. The resulting
+inventory retained all ten default-branch source/target snapshots, totaling
+9,023,076,490 bytes. No cache quota or runner-plan setting changed.
+
+This retires one upstream registration, not arbitrary future workflow files.
+New auxiliary workflows and any re-enablement still need resource/ownership review.
+Dependency or SDK changes can legitimately cause cold builds; cache retention does
+not establish a fixed CI duration.
+
+## Validation
+
+- The disable API returned 204; a fresh GET reported `disabled_manually` for
+  upstream workflow `366570225` and `active` for fork workflow `366585525`.
+- No screenshot run was active or queued, so no workflow run was cancelled.
+- Deleting cache `8179623547` returned 204. Readback showed the selected PR cache
+  absent and every pre-cleanup default-branch cache ID still present.
+- The main-branch rules read before and after the operation were identical.
+- The preceding main native run [36362067181](https://github.com/Kuddev/pebrel/actions/runs/36362067181)
+  completed successfully and repopulated the shared snapshots. A subsequent PR
+  run measures reuse; this operation does not claim that the eight-minute target
+  has already been achieved.
+
+## Supersedes
+
+None. The coverage and cache boundaries in
+[shared native PR caches](2026-09-25-shared-native-pr-cache.md) and
+[shared macOS runners](2026-09-27-shared-macos-runners.md) remain unchanged.
+
+## Revisit when
+
+An upstream-owned screenshot workflow has an agreed opt-in trigger, source identity
+and bounded read-only cache use. Re-enabling the recorded registration requires an
+explicit maintainer action after that review; a documentation edit is not an
+enablement operation.