[rbuergi]

Root-causes and fixes #1692 — the recurrence of the CollectionNamedArea empty-render flake (CollectionNamedArea_RendersBrowserForFolder_AndContentForFile, run 31972489250: last emission MarkdownControl { Markdown = <empty>, Html = <empty> }).

Root cause

#978 established the trigger-order rule (a monotonic sequence claimed at trigger time; an ingest may only merge if no later-triggered ingest of the same file already landed), but it checked the claim on the pool read-completion thread and posted the merge afterwards — the apply happens later, serialized on the sync hub via UpdateStreamRequest. Claim and apply were not atomic:

1. The watcher's Created-event ingest triggers while the just-created file is still 0 bytes (share-tolerant reads are by design — see FileSystemStreamProvider.WriteStreamAsync); it parses an EMPTY article and passes its claim on its pool thread.
2. Before its markdownStream.Update post enqueues (a window fattened by Update()'s context-capture fallback chain — DI lookups between claim and post), SaveFile's later-triggered read-your-writes ingest claims and posts the complete article.
3. The hub applies complete-then-torn: apply order inverts claim order, the empty article lands last and sticks — and on Linux, inotify drops events for files written into a just-created subdirectory, so no repair event ever comes. The render serves the empty MarkdownControl forever.

Both prior fixes (#238 read-your-writes, #978 trigger-order claim) are intact and necessary — this closes the residual check-then-act window between them.

Fix

ClaimIngest is now evaluated inside the update transform, which the sync hub invokes strictly serially — claim and apply are atomic, so apply order can never invert claim order. A superseded ingest's transform returns null, which SetCurrent skips as a no-op. The merge is extracted as the protected virtual MergeIngestedArticle boundary.

Deterministic red-proven pin

ContentCollectionClaimApplyRaceTest removes the timing entirely: a collection subclass holds the torn ingest at exactly the defect's window (post-parse/post-claim, pre-post), lets the later-triggered complete article provably apply, then releases the held merge.

• RED under pre-fix semantics (claim in callback, unconditional apply — verified locally against that variant): the released empty article overwrites the complete one — assertion fails with found "", the exact CI signature.
• GREEN with the fix: the claim, evaluated at apply time under the stream's serialization, drops it.

Verification

• ContentCollectionClaimApplyRaceTest: red on pre-fix variant, green on fix (fresh .trx each)
• Full MeshWeaver.ContentCollections.Test: 30/30 passed (includes the originally-failing NodeHubContentCollectionTest)
• dotnet build -c Release -warnaserror: clean for MeshWeaver.ContentCollections, its test project, and MeshWeaver.Documentation
• What's New entry included (Category: Fix) — users historically saw "upload a file, open it, page is empty"

Closes #1692

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes a race in ContentCollection where a stale/empty ingest (often from a watcher Created event) could incorrectly overwrite a later-triggered “read-your-writes” ingest, leading to permanent empty renders for newly uploaded markdown files. It makes the trigger-order “claim” check atomic with the stream apply by evaluating it inside the synchronization stream’s serialized update transform, and adds a deterministic test to pin the interleaving.

Changes:

• Move ingest-order claim evaluation into the stream update transform via a new MergeIngestedArticle boundary, ensuring claim/apply atomicity.
• Add a deterministic regression test that forces the pre-fix interleaving without timing dependence.
• Add a “What’s New” entry documenting the user-visible fix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/MeshWeaver.ContentCollections/ContentCollection.cs	Makes ingest claim evaluation atomic with stream application by performing it inside the serialized update transform (MergeIngestedArticle).
test/MeshWeaver.ContentCollections.Test/ContentCollectionClaimApplyRaceTest.cs	Adds a deterministic test that reproduces the claim/apply overtaking window and verifies stale ingests cannot overwrite newer content.
src/MeshWeaver.Documentation/Data/WhatsNew/2026-08-16-content-upload-empty-render-race.md	Documents the fix as a user-facing “Fix” entry in What’s New.

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[github-actions]

Test Results (shard 0)

920 tests   919 ✅  11m 2s ⏱️
 10 suites    1 💤
 10 files      0 ❌

Results for commit 0220e35.

[github-actions]

Test Results (shard 5)

1 371 tests   1 370 ✅  5m 45s ⏱️
   11 suites      1 💤
   11 files        0 ❌

Results for commit 0220e35.

[github-actions]

Test Results (shard 4)

1 606 tests   1 600 ✅  7m 19s ⏱️
   11 suites      6 💤
   11 files        0 ❌

Results for commit 0220e35.

[github-actions]

Test Results (shard 3)

   11 files     11 suites   5m 54s ⏱️
2 197 tests 2 006 ✅ 191 💤 0 ❌
2 567 runs  2 376 ✅ 191 💤 0 ❌

Results for commit 0220e35.

[github-actions]

Test Results (shard 1)

2 164 tests   2 061 ✅  7m 19s ⏱️
   11 suites    103 💤
   11 files        0 ❌

Results for commit 0220e35.

[github-actions]

Test Results (shard 2)

2 447 tests   2 443 ✅  7m 41s ⏱️
   11 suites      4 💤
   11 files        0 ❌

Results for commit 0220e35.

[github-actions]

Test Results

    65 files      65 suites   45m 2s ⏱️
10 705 tests 10 399 ✅ 306 💤 0 ❌
11 075 runs  10 769 ✅ 306 💤 0 ❌

Results for commit 0220e35.