improvement(staging-mode): Clarify Squash/Rollback behavior for ContainerMessageType.GC

[markfields]

Description

GC ops can be made while in Staging Mode, and we need to be very clear with how they're handled.

• Squashing: They don't need to be squashed, no personal data to protect
• Rollback: GC ops submitted while in Staging Mode will be dropped if staged changes are discarded. (these are all "Tombstone Loaded" ops, which prevent data loss in case of invalid GC data)
  • We will log a new error event GC_OpDiscarded to highlight this case
  • We are also adding a prop inStagingMode to all ContainerRuntime logs, including GC_Tombstone_DataStore_Requested etc, to further aid investigations
  • Note: In our largest 1P customer depending on GC, there are no outstanding root causes leading to Tombstone Load events (where we depend on the GC op to avoid data loss). So we should not see this at all until something else regresses in GC, at which point the new info logged will come to bear in the investigation.

Also refactor the Resubmit code so it's clear that being able to support squash is an exceptional case - most op types don't need to deal with it.

Reviewer Guidance

This was pulled out of #24729 since it's really a separate change.

[Copilot]

Pull Request Overview

This PR clarifies how GC operations behave in Staging Mode and refactors the resubmit logic to treat squash support as an exceptional case.

• Enhance IPendingMessage with clearer metadata fields for op submission and sequencing.
• Add explanatory comments around GC tombstone telemetry and staging behavior.
• Refactor ContainerRuntime to introduce isSummarizerClient, wire it through lifecycle paths, and separate squash vs. non-squash resubmit flows.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/runtime/container-runtime/src/pendingStateManager.ts	Added localOpMetadata, opMetadata, and sequenceNumber fields with comments.
packages/runtime/container-runtime/src/gc/garbageCollection.ts	Expanded comment to list the telemetry events preceding tombstone load errors.
packages/runtime/container-runtime/src/containerRuntime.ts	Introduced isSummarizerClient; updated monitoring context; refactored reSubmitBatch, reSubmitWithSquashing, and reSubmit to distinguish squash paths and GC/DocumentSchemaChange handling.

Comments suppressed due to low confidence (4)

packages/runtime/container-runtime/src/pendingStateManager.ts:57

• The localOpMetadata field is typed as unknown. Consider defining and using a more specific interface to improve type safety and documentation of expected metadata shape.

localOpMetadata: unknown;

packages/runtime/container-runtime/src/gc/garbageCollection.ts:1048

• [nitpick] The comment starts with lowercase "i.e."; for consistency and readability, consider capitalizing the first letter or rephrasing to begin a new sentence.

// i.e. this will be preceded by one of these telemetry events;

packages/runtime/container-runtime/src/containerRuntime.ts:1189

• Public or private properties injected in multiple lifecycle paths benefit from a doc comment explaining their purpose, especially isSummarizerClient since it alters teardown and resubmit behavior.

private readonly isSummarizerClient: boolean;

packages/runtime/container-runtime/src/containerRuntime.ts:4680

• The new squash vs. non-squash code paths (reSubmitWithSquashing vs. reSubmit) introduce conditional behavior for GC and schema ops. Ensure unit tests cover each branch, including GC being forwarded or dropped under squash.

const resubmitFn = squash

[agarwal-navin]

How come you added a hex code here? Is this copilot generated?

[markfields]

It's just a move from LHS line 4687

[agarwal-navin]

Is it possible to log more details here such as the id of the object, pkg, etc? That will help debugging if and when we see this log. As of now, debugging this will be very hard.

[markfields]

I think it'll be ok because there will be a corresponding GC_Tombstone_DataStore_Requested (or other object) event with more info