docs: document the R3 1.3.1 limitations of bind, catch and mapAsync

[xperiandri]

Proposed Changes

Part of splitting #22 into small pull requests that can be reviewed one at a time. It is stacked on #41 (docs/async-task), so it shows only its own change; merge #41 first.

Documentation only. Writing the integration tests of #22 exposed R3 1.3.1 defects that the library cannot work around without reimplementing the operators, so the docs state them where they apply:

• bind: an inner failure after the source completed is ignored, so the result completes without it, or never completes when it was the last inner sequence running – SelectMany drops an inner failure that arrives after the source completed Cysharp/R3#401.
• catch: disposing the result after it switched to the handler's sequence leaves that sequence subscribed – Catch does not unsubscribe from the handler's sequence when disposed Cysharp/R3#400.
• mapAsync, both flavours: a failure after the source completed is dropped (SelectAwait and SubscribeAwait do not properly propagate exception to UnhandledExceptionHandler Cysharp/R3#377), an OperationCanceledException is never reported and stops the sequential modes (SelectAwait/SubscribeAwait swallow every OperationCanceledException and stop the sequential modes for good Cysharp/R3#399), and every failure of a limited AwaitSequentialParallel leaks a slot (SelectAwait with AwaitOperation.SequentialParallel and maxConcurrent leaks a slot when the selector fails Cysharp/R3#397).

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

iterAsync is not affected by the mapAsync limitations since #38.

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
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 ← this pull request
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

🟢 Approval recommended

The documentation accurately reflects the referenced R3 1.3.1 defects and follows the project’s XML documentation conventions.

Review effort: Balanced
Findings: None

What changed in this PR

Documents known R3 1.3.1 limitations affecting observable operators.

Changes:

• Documents bind and catch failure/disposal defects.
• Documents mapAsync failure, cancellation, and concurrency-slot defects.
• Updates the changelog.

File	Description
CHANGELOG.md	Records the added limitation documentation.
Observable.fs	Documents bind and catch limitations.
AsyncObservable.fs	Documents Async mapAsync limitations.
TaskObservable.fs	Documents Task mapAsync limitations.

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