fix(async)!: surface the original exception and cancellation from Async wrappers

[xperiandri]

Proposed Changes

Part of splitting #22 into small pull requests that can be reviewed one at a time. It is stacked on #35 (fix/async-to-lookup-token), so it shows only its own change; merge #35 first.

Every Async terminal function ended with Async.AwaitTask, which raises the AggregateException of a faulted task and turns a cancelled task into a failure. try ... with :? InvalidOperationException inside async therefore never matched, while the Task flavour surfaced the R3 exception directly.

An internal helper keeps Async.AwaitTask, which resumes on the synchronization context that was current when the computation started to wait, and only translates its outcome: the single inner exception of an AggregateException is raised through the continuations, which keeps its stack trace, and a cancelled task cancels the computation. Both flavours now have the same error surface. toArray is no longer inline, because the helper is internal.

Types of changes

What types of changes does your code introduce to FSharp.Control.R3?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• Build and tests pass locally – 0 warnings, Fantomas is clean, and the tests that exist at this commit pass
• I have added tests that prove my fix is effective or that my feature works (if appropriate) – in test: cover the library with integration tests #22, the top of this stack
• I have added necessary documentation (if appropriate)

Further comments

The module docs that describe this error surface come with the Async and Task docs in #41.

Breaking change: code that caught AggregateException from the Async functions now receives the inner exception, and a cancelled operation cancels the computation instead of failing it.

Tests (in #22): AsyncObservableTests.fs – firstAsync of an empty source raises InvalidOperationException rather than an AggregateException, the data-row tests of every terminal function (the same exception instance, cancellation, an already cancelled token) and a terminal function resumes on the synchronization context that was current when it started to wait.

Stack – every pull request is based on the one before it, so each shows only its own change. Merge them in this order:

1. refactor!: prefix AwaitOperationConfiguration cases with Await #23 refactor!: prefix AwaitOperationConfiguration cases with Await
2. fix: validate the concurrency limit of mapAsync options eagerly #24 fix: validate the concurrency limit of mapAsync options eagerly
3. fix(rxquery): emit yield/zero synchronously to keep element order #25 fix(rxquery): emit yield/zero synchronously to keep element order
4. fix(rxquery)!: stop seeding sumBy with Unchecked.defaultof #26 fix(rxquery)!: stop seeding sumBy with Unchecked.defaultof
5. feat(rxquery): add rxqueryWith to cancel the terminal query operators #27 feat(rxquery): add rxqueryWith to cancel the terminal query operators
6. docs(rxquery): document the query builder and every query operator #28 docs(rxquery): document the query builder and every query operator
7. feat(observable)!: make ofSeq reachable as Observable.ofSeq #29 feat(observable)!: make ofSeq reachable as Observable.ofSeq
8. feat(observable)!: make Observable.choose take a voption chooser, add ObservableOption #30 feat(observable)!: make Observable.choose take a voption chooser, add ObservableOption
9. feat(observable): add chunkByBoundaries for boundaries of any element type #31 feat(observable): add chunkByBoundaries for boundaries of any element type
10. fix(observable): validate every chunk length eagerly #32 fix(observable): validate every chunk length eagerly
11. docs: document the processing and chunk configuration types #33 docs: document the processing and chunk configuration types
12. docs(observable): correct misleading XML docs and document every function #34 docs(observable): correct misleading XML docs and document every function
13. fix(async)!: remove the ignored cancellationToken from toLookup #35 fix(async)!: remove the ignored cancellationToken from toLookup
14. fix(async)!: surface the original exception and cancellation from Async wrappers #36 fix(async)!: surface the original exception and cancellation from Async wrappers ← this pull request
15. fix: wait for iterAsync through ForEachAsync instead of CountAsync #37 fix: wait for iterAsync through ForEachAsync instead of CountAsync
16. fix: stop iterAsync reliably and never lose a failure of its action #38 fix: stop iterAsync reliably and never lose a failure of its action
17. fix(task)!: default ofTask configureAwait to true #39 fix(task)!: default ofTask configureAwait to true
18. feat(task)!: move toArray and toList into the Task.Observable module #40 feat(task)!: move toArray and toList into the Task.Observable module
19. docs: correct the Async and Task module docs and document every member #41 docs: correct the Async and Task module docs and document every member
20. docs: document the R3 1.3.1 limitations of bind, catch and mapAsync #42 docs: document the R3 1.3.1 limitations of bind, catch and mapAsync
21. test: categorize the tests per tested component #43 test: categorize the tests per tested component
22. test: cover the library with integration tests #22 test: cover the library with integration tests

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🟡 Changes recommended

The new fault, cancellation, and synchronization-context behavior needs tests in this independently merged PR.

Review effort: Balanced
Findings: 1

Open (1)

• Add fault, cancellation, and synchronization-context test coverage · New

What changed in this PR

Updates Async terminal wrappers to propagate original exceptions and cancellation consistently with Task wrappers.

Changes:

• Adds shared task-awaiting interoperability helpers.
• Applies them to all Async terminal functions.
• Documents the breaking behavior change.

File	Description
src/​FSharp.Control.R3/​AsyncObservable.fs	Translates task faults and cancellation into Async outcomes.
CHANGELOG.md	Records the breaking error-surface change.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.