ably: deprecate releasing a realtime channel that isn't detached (RTS4b)

[SimonWoolf]

Implements RTS4b from spec 6.3.0 (ably/specification#557).

Spec 6.3.0 replaces RTS4a, under which Channels.Release detaches a channel before removing it, with RTS4c–e, under which releasing a channel that isn't INITIALIZED, DETACHED or FAILED is an error (90011). RTS4b lets us keep the old behaviour until the next major version, provided we log a deprecation warning.

• RealtimeChannels.Release now logs a deprecation warning when called on a channel that is not INITIALIZED, DETACHED or FAILED, then detaches and releases it as before.
• A channel already in one of those states is now removed without attempting a detach (RTS4d). Previously Release always called Detach, so it returned an error and left the channel in the collection when the channel was FAILED (RTL5b) or the connection was CLOSING or FAILED (RTL5g).
• Docstring updated: a realtime channel should only be released when it is in the INITIALIZED, DETACHED or FAILED state.

To avoid the warning, call channel.Detach(ctx) and wait for it to return before calling client.Channels.Release(ctx, name).

The next-major change is in #717. Reference ably-js PRs: ably/ably-pubsub-js#2322 (deprecation) and ably/ably-pubsub-js#2323 (next major).

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Releasing a channel that doesn’t exist now completes without an error.
  • Channels in releasable states are removed without being detached. Channels in other states are detached before removal, and remain available if detaching fails.

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📥 Commits

Reviewing files that changed from the base of the PR and between b29111c and 781e5c2.

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📒 Files selected for processing (4)

• ably/realtime_channel.go
• ably/realtime_channel_integration_test.go
• ably/realtime_channel_internal_test.go
• ably/state.go

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Walkthrough

RealtimeChannels.Release now checks channel state before removal. It removes releasable states directly. For other states, it logs a deprecation warning, detaches the channel, and returns any detach error.

Changes

Channel release behavior

Layer / File(s)	Summary
State-aware release ably/state.go, ably/realtime_channel.go, ably/realtime_channel_internal_test.go, ably/realtime_channel_integration_test.go	ChannelState.canRelease identifies INITIALIZED, DETACHED, and FAILED as releasable states. Release removes those channels without detaching. For other states, it logs a deprecation warning and detaches before removal. Internal tests cover missing channels and state-specific outcomes; the integration test comment identifies the behavior as deprecated under RTS4b.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: lmars

Merge Risk: 🟡 Moderate · up to b2911

A concurrent attach can leave a channel attached after release. Coordinate attachment and removal before merging.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 20.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly identifies the main change: deprecating release of a realtime channel that is not detached under RTS4b. This matches the implementation and stated objectives.

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_{A rabbit checks each channel state,
Then lets releasable ones vacate.
Others get a warning first,
Then detaching breaks the burst.
The burrow logs each change with care.}

_{Comment @coderabbitai help to get the list of available commands.}

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
minimal, and validate.

Inline comments:
Review comments at @ably/realtime_channel.go:
- Line 219: Update Release’s state check and channel removal to synchronize with
Attach, keeping the synchronization in place until the channel has been removed
so a concurrent attach cannot leave the channel attached after removal.

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📥 Commits

Reviewing files that changed from the base of the PR and between 26cb171 and b29111c.

📒 Files selected for processing (4)

• ably/realtime_channel.go
• ably/realtime_channel_integration_test.go
• ably/realtime_channel_internal_test.go
• ably/state.go

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[ttypic]

LGTM