feat: subscription locate mode

[CarlosGamero]

What

1. New locateOnly mode for subscriptions

subscriptionConfig: {
  locateOnly: true,
  managedAttributes: ['FilterPolicy', 'FilterPolicyScope'],
  Attributes: { FilterPolicy: JSON.stringify({ type: ['entity.created'] }) },
}

The library finds the subscription but never creates or deletes it. It only updates the attributes it manages.
The topic and the queue must be located too.

Why: when other tools own the subscription, the service still needs to own the filter policy, because it comes from
the consumer handlers.

2. Only write what changed (#618)

The library reads the subscription attributes first and only writes the ones that are different.
managedAttributes says which attributes the service owns (default: all). Missing managed attributes are reset.

Why: before, every startup wrote to the subscription, and removed attributes were never cleaned up.

3. locatorConfig.subscriptionArn is deprecated

Why: the subscription is now found from the topic and the queue, so the ARN is not needed.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Existing SNS-to-SQS subscriptions can now be located without creating them, with configured attributes applied to the located subscription.
  • Managed subscription attributes are reconciled with configured values, including resetting omitted managed attributes to defaults. Unmanaged attributes are left unchanged.
  • Non-blocking startup callbacks now wait until the topic, queue, and subscription are available.

• Documentation

  • Clarified locate-only requirements, subscription attribute management, and behavior when using a consumer’s dead-letter queue for subscription redrive settings.

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📝 Walkthrough

Walkthrough

The change adds locate-only SNS subscription resolution and managed-attribute reconciliation. It updates SNS/SQS consumer lifecycle handling for locate-only subscriptions and DLQ redrive policies, and revises documentation and tests.

Changes

SNS subscription management

Layer / File(s)	Summary
Subscription attribute contracts and reconciliation packages/sns/lib/utils/snsSubscriber.ts, packages/sns/lib/utils/snsSubscriber.spec.ts, packages/sns/lib/index.ts, packages/sns/README.md, packages/sns/test/utils/fauxqsInstance.ts	Subscription options now distinguish creation from locate-only mode and support managed attributes. Existing attributes are compared with configured values, and only differences are written. Managed attributes omitted from configuration are reset to SNS defaults.
Locate-only subscription resolution packages/sns/lib/utils/snsInitter.ts, packages/sns/lib/utils/snsInitter.spec.ts, packages/sns/lib/utils/snsUtils.ts, README.md, packages/sns/README.md	The initializer resolves confirmed subscriptions from topic and queue locators. Locate-only mode applies configured attributes and requires both resources to be located. Examples and documentation describe the revised resolution and polling behavior.
Consumer lifecycle and DLQ handling packages/sns/lib/sns/AbstractSnsSqsConsumer.ts, packages/sns/test/consumers/SnsSqsPermissionConsumer.spec.ts, packages/sqs/lib/sqs/AbstractSqsConsumer.ts	Locate-only mode skips subscription and queue deletion. When the consumer DLQ is reused for the subscription, the consumer removes RedrivePolicy from subscription configuration and sets it after DLQ initialization.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant Consumer
  participant initSnsSqs
  participant findConfirmedSubscriptionArn
  participant setSubscriptionAttributes
  participant SNS
  Consumer->>initSnsSqs: Initialize with locateOnly configuration
  initSnsSqs->>findConfirmedSubscriptionArn: Find subscription for topic and queue
  findConfirmedSubscriptionArn->>SNS: Look up matching subscription
  SNS-->>findConfirmedSubscriptionArn: Return confirmed subscription ARN
  findConfirmedSubscriptionArn-->>initSnsSqs: Return ARN
  initSnsSqs->>setSubscriptionAttributes: Apply configured attributes
  setSubscriptionAttributes->>SNS: Read and update differing attributes
  SNS-->>setSubscriptionAttributes: Return subscription attributes
  setSubscriptionAttributes-->>initSnsSqs: Complete attribute reconciliation
  initSnsSqs-->>Consumer: Return subscription ARN

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Suggested reviewers: kibertoad

Merge Risk: 🟡 Moderate · up to 53bda

Existing subscriptions may fail to initialize or lose their dead-letter policy after an upgrade. Preserve the previous creation-mode behavior or provide explicit migration guidance before merging.

Security Architecture Review

Security architecture risk: 🟡 Moderate · up to 53bda

Existing configurations can now reset subscription filters or dead-letter policies that were previously preserved. The deprecated subscription ARN also permits updates without checking its relationship to the located topic and queue. Explicit attribute ownership and deletion guards reduce risk, but configuration trust and AWS permission scope remain unresolved.

Retained concerns

• Medium · architecture · observed: The new default assumes ownership of every supported subscription attribute. Existing callers that omit attributes can now remove an existing filter or RedrivePolicy when updates are enabled, rather than preserving external configuration. Locate-only callers have the same reset behavior unless they narrow managedAttributes. This can broaden message delivery or remove failure capture; documentation and explicit ownership configuration mitigate, but do not preserve, the previous default.
• Medium · security · inferred: A supplied deprecated subscriptionArn bypasses the topic/queue lookup but still receives locate-only attribute writes. A mismatched ARN can therefore redirect filter or redrive changes to a subscription unrelated to the located resources, if the configured AWS identity permits the operation. The ordinary lookup path avoids this shortcut. Caller configuration trust and IAM scope are unknown, so unauthorized reachability is not established.

Security review details

Security Blast Radius

• inferred — Each reconciliation targets one selected subscription. With the legacy ARN shortcut, possible mutation scope is bounded by the configured AWS identity's effective permissions rather than by the located topic and queue. Repository evidence does not establish tenant, account, or environment isolation for those permissions.

Security Findings and Attack Paths

• inferred — If a less-trusted caller can influence subscriptionArn and the SNS client can write other subscriptions, that input can redirect locate-only filter or redrive updates to another asset. Source establishes the configuration-to-write path, but not the less-trusted caller or permissive IAM prerequisites; this remains a conditional architecture concern.

Trust Boundaries and Controls

• observed — The ordinary subscription-resolution path supplies the resolved topic and queue ARNs to confirmed-subscription lookup. Locate-only consumer deletion guards preserve the located resources, while managedAttributes provides an explicit attribute-level ownership boundary. Supplying a legacy ARN bypasses the lookup portion of that boundary.

Resilience and Maintainability Implications

• observed — Background resource-reconciliation rejection terminates that resolution attempt without invoking readiness and is reported as a final error. After readiness, however, the consumer's non-blocking callback logs a DLQ initialization failure and can still start consumers. That catch-and-continue behavior is present in available older source and is not treated as newly introduced by this PR.

Hardening Proposals

• proposed — Before enabling reconciliation on an externally owned subscription, explicitly select application-owned attributes and retain an authoritative configuration for restoring filter and redrive values after an interrupted upgrade or rollback.
• proposed — Validate a supplied legacy subscription ARN against the resolved topic, queue endpoint, and expected protocol before mutation, or reject the shortcut when locate-only reconciliation is requested.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 52.63% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 10 files. (2 skipped:…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding subscription locate mode.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 52.63% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 10 files. (2 skipped: 2 unsupported.)

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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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Inline comments:
Review comments at @packages/sns/lib/utils/snsSubscriber.ts:
- Line 281: Update the managed-attribute defaulting around
resolvedManagedAttributes so creation mode manages only attributes present in
subscribeInput.Attributes when managedAttributes is omitted, preserving existing
omitted subscription attributes; retain the documented default behavior for
locate-only mode.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: 9f95498e-d7c5-4354-a7fa-5a88d5ee83f0

📥 Commits

Reviewing files that changed from the base of the PR and between 68a5a52 and 53bdae9.

⛔ Files ignored due to path filters (1)

• pnpm-lock.yaml is excluded by !**/pnpm-lock.yaml

📒 Files selected for processing (12)

• README.md
• packages/sns/README.md
• packages/sns/lib/index.ts
• packages/sns/lib/sns/AbstractSnsSqsConsumer.ts
• packages/sns/lib/utils/snsInitter.spec.ts
• packages/sns/lib/utils/snsInitter.ts
• packages/sns/lib/utils/snsSubscriber.spec.ts
• packages/sns/lib/utils/snsSubscriber.ts
• packages/sns/lib/utils/snsUtils.ts
• packages/sns/test/consumers/SnsSqsPermissionConsumer.spec.ts
• packages/sns/test/utils/fauxqsInstance.ts
• packages/sqs/lib/sqs/AbstractSqsConsumer.ts

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