docs: update queue documentation for fan-out delivery semantics

[ytallo]

Summary

• module-queue.mdx: Updated topic-based queues section with fan-out per function explanation, added fan-out delivery Info callout, new Delivery row in comparison table, RabbitMQ per-function queue naming table, topic-based fan-out sequence diagram, and updated enqueue builtin function description.
• module-pubsub.mdx: Fixed PubSub vs Queue comparison table — "Single consumer per message" was incorrect after fan-out; now correctly reads "Fan-out to each subscribed function; replicas of the same function compete".
• use-queues.mdx: Comprehensive rewrite covering what queues are, when to use/avoid, both queue modes (topic-based + named), fan-out delivery model with diagrams, condition filtering, and four real-world scenarios (HTTP-to-queue pipeline, event fan-out, FIFO ledger, bulk email rate limiting).

Follows up on #1384 (feat: queue fan-out per function).

Test plan

• Verify docs render correctly on preview deployment
• Confirm all internal cross-references resolve (use-queues, module-queue, dead-letter-queues, trigger-actions, conditions)
• Review mermaid diagrams render in the docs site

Summary by CodeRabbit

• Documentation
  • Clarified queue delivery semantics, including topic-based fan-out behavior where messages are delivered to each subscribed function
  • Expanded queue guides with new real-world scenarios covering event fan-out and rate limiting patterns
  • Enhanced PubSub vs Queue comparison table with updated delivery model descriptions
  • Added documentation for message filtering via conditions and fan-out delivery model clarifications

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Project	Status	Preview	Updated (UTC)
iii	🟢 Ready	View Preview	Apr 2, 2026, 12:47 AM

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Project	Deployment	Actions	Updated (UTC)
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motia-docs	Ready	Preview, Comment	Apr 2, 2026 0:47am

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 6f6feac8-a8fb-428a-8871-064db6f8ed3f

📥 Commits

Reviewing files that changed from the base of the PR and between f5ac693 and 6f637f0.

📒 Files selected for processing (3)

• docs/how-to/use-queues.mdx
• docs/modules/module-pubsub.mdx
• docs/modules/module-queue.mdx

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📝 Walkthrough

Walkthrough

Documentation restructured to distinguish topic-based queues (fan-out to multiple subscribed functions with competing replicas) from named queues (FIFO acknowledgment-based). Updated queue delivery semantics explanation, added fan-out delivery diagrams, and revised real-world scenarios and comparison tables across queue and pubsub modules.

Changes

Cohort / File(s)	Summary
Queue delivery semantics documentation docs/how-to/use-queues.mdx, docs/modules/module-queue.mdx	Restructured to define topic-based queues with fan-out semantics (each subscribed function receives a copy, replicas compete per function) and named queues with FIFO/acknowledgment behavior. Added message filtering via conditions, sequence diagrams for topic-based and named queue flows, clarified RabbitMQ adapter naming conventions, and rewrote real-world scenarios to reflect the two queue modes.
PubSub comparison clarification docs/modules/module-pubsub.mdx	Updated queue vs. pubsub comparison table to specify queue behavior as "topic-based" with fan-out to subscribed functions and retries/dead-letter support, while clarifying pubsub as "fire-and-forget fanout."

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• feat: update documentation structure for trigger actions and queues #1327: Modifies the same queue documentation files and adjusts how queues, trigger actions, and delivery semantics are described.

Suggested reviewers

• andersonleal

Poem

🐰 Queues now split in two, so clear—
Topics fan-out without a fear!
Named ones ordered, replicas compete,
Dead letters catch what's not so sweet.
Docs bloom bright with diagrams new, 🐇✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: comprehensive updates to queue documentation to explain fan-out delivery semantics across three key documentation files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/queue-fanout-documentation

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