fix(driver-utils): prevent unhandled rejection in getSnapshotTree prefetch

[anthony-murphy-agent]

Summary

• Fix unhandled promise rejections in PrefetchDocumentStorageService fire-and-forget calls
• Add unit test for getSnapshotTree failure scenario

Problem

This is a follow-up to PR #26151. After that fix was deployed, telemetry showed 349 uncaughtException errors from ShreddedSummaryDocumentStorageService.readBlob in test-service-load tinylicious tests.

Root cause: PR #26151 attached .catch() to the inner promise in cachedRead(), but that only handles ONE promise chain. The fire-and-forget callers create a DIFFERENT chain:

1. void this.cachedRead(blob) - cachedRead is async, so it returns a NEW promise wrapping the inner promise. The .catch() on the inner promise doesn't prevent unhandled rejection on the async function's returned promise.

2. void p.then(...) in getSnapshotTree() - creates a derived promise that also rejects when p rejects.

Solution

Fix all three fire-and-forget patterns:

// Before (inner promise handled, but async wrapper not):
void this.cachedRead(blob);

// After (handles the async function's returned promise):
this.cachedRead(blob).catch(() => {});

// Before (derived promise not handled):
void p.then((tree) => this.prefetchTree(tree));

// After (handles the derived promise):
void p.then(...).catch(() => {});

Test plan

• New unit test for getSnapshotTree failure scenario
• All 5 PrefetchDocumentStorageService tests pass
• Build passes

🤖 Generated with Claude Code

Co-Authored-By: anthony-murphy [email protected]

[anthony-murphy]

/azp run Build - api-markdown-documenter, Build - benchmark-tool, Build - build-common, Build - build-tools, Build - client packages, Build - common-utils, Build - eslint-config-fluid, Build - eslint-plugin-fluid, Build - protocol-definitions, Build - test-tools

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Azure Pipelines successfully started running 1 pipeline(s).

[anthony-murphy]

/azp run repo-policy-check, server-gitrest, server-gitssh, server-historian, server-routerlicious

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[Copilot]

Pull request overview

This PR fixes an unhandled promise rejection bug in PrefetchDocumentStorageService.getSnapshotTree() by adding a .catch() handler to the fire-and-forget prefetch pattern. This is a follow-up to PR #26151, which fixed a similar issue in cachedRead() but missed this code path.

• Adds .catch() handler to prevent unhandled rejections when getSnapshotTree() fails
• Adds unit test to verify the fix and ensure errors are still properly propagated to callers

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/loader/driver-utils/src/prefetchDocumentStorageService.ts	Adds .catch() handler to fire-and-forget prefetch pattern in getSnapshotTree() to prevent unhandled rejections while still propagating errors to callers
packages/loader/driver-utils/src/test/prefetchDocumentStorageService.spec.ts	Adds mock failure flags and test case to verify getSnapshotTree() failures don't cause unhandled rejections

[anthony-murphy-agent]

Azure Pipelines commands (copy and post separately, limit of 10 at a time):

/azp run Build - api-markdown-documenter, Build - benchmark-tool, Build - build-common, Build - build-tools, Build - client packages, Build - common-utils, Build - eslint-config-fluid, Build - eslint-plugin-fluid, Build - protocol-definitions, Build - test-tools

/azp run repo-policy-check, server-gitrest, server-gitssh, server-historian, server-routerlicious

[anthony-murphy]

/azp run Build - api-markdown-documenter, Build - benchmark-tool, Build - build-common, Build - build-tools, Build - client packages, Build - common-utils, Build - eslint-config-fluid, Build - eslint-plugin-fluid, Build - protocol-definitions, Build - test-tools

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[anthony-murphy]

/azp run repo-policy-check, server-gitrest, server-gitssh, server-historian, server-routerlicious

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.