Compress large telemetry properties with gzip chunked columns

[vijayupadya]

Fixes https://github.com/microsoft/vscode-internalbacklog/issues/8434

What

Adds gzip + base64 compression for oversized telemetry properties in both the Copilot extension and the agent host, replacing the previous plain string-splitting for known-large fields.

When a property exceeds MAX_PROPERTY_LENGTH (8192 chars) — or is one of the always-compressed keys (messagesJson, diffsJSON) — the original column now carries only the first uncompressed 8192-char slice, and the full value is gzip-compressed, base64-encoded, and emitted across <key>Chunk, <key>Chunk_2, … columns (up to MAX_CONCATENATED_PROPERTIES). Values under the limit that aren't force-compressed are unchanged, and when no compressor is available the code falls back to the original plain continuation family.

Why

Large prompt/message/diff payloads previously inflated telemetry volume as raw split strings. Compressing them significantly reduces the emitted size while keeping a uniform, backend-readable chunk layout.

How

• multiplexProperties is now async and awaits a pluggable compressor. The extension registers a gzip (via util.promisify(zlib.gzip)) + base64 compressor through setTelemetryPropertyCompressor; the agent host uses the same approach via compressTelemetryValue.
• All call sites that build telemetry properties now use a fire-and-forget pattern (void multiplexProperties(...).then(send).catch(() => { /* best-effort telemetry */ })) so gzip runs off the event loop and never blocks hot paths (request dispatch, tool calls, inline edits).
• The agent host telemetry reporter and GitHub telemetry router were made async to await multiplexing before routing.

Testing

• Updated telemetry.spec.ts compression tests to async and added coverage for the chunked-column layout.
• Updated agent host tests (agentHostGitHubTelemetryRouter, agentHostRepoInfoTelemetry, agentHostTelemetryReporter) for the async flow.
• All telemetry unit tests pass; no compile errors.

[Copilot]

Pull request overview

Adds gzip/base64 compression and chunking for oversized telemetry properties across Agent Host and Copilot extension telemetry paths.

Changes:

• Introduces asynchronous compressed property multiplexing.
• Updates telemetry senders and routers for asynchronous processing.
• Adds compression and round-trip tests.

Show a summary per file

File	Description
agentHostTelemetryReporter.test.ts	Updates reporter tests for async compression.
agentHostRepoInfoTelemetry.test.ts	Updates reporter mocks to async.
agentHostGitHubTelemetryRouter.test.ts	Tests compressed routing and round-tripping.
agentHostTelemetryReporter.ts	Compresses restricted telemetry properties.
agentHostRestrictedTelemetry.ts	Implements Agent Host gzip chunking.
agentHostGitHubTelemetryRouter.ts	Makes telemetry routing asynchronous.
telemetryServiceImpl.ts	Registers the Node gzip compressor.
telemetry.spec.ts	Adds compression behavior tests.
telemetry.ts	Implements shared compressed multiplexing.
chatStream.ts	Sends multiplexed telemetry asynchronously.
multiFileEditQualityTelemetry.ts	Adapts edit telemetry to async multiplexing.
applyPatchTool.tsx	Adapts patch telemetry to async multiplexing.
abstractReplaceStringTool.tsx	Adapts replacement telemetry to async multiplexing.
codeMapper.ts	Adapts successful-edit telemetry.
repoInfoTelemetry.ts	Adapts repository telemetry.
chatMLFetcher.ts	Adapts tool-option telemetry.
nextEditProviderTelemetry.ts	Adapts next-edit telemetry.
continuousEnhancedTelemetrySender.ts	Adapts continuous telemetry.

Review details

• Files reviewed: 18/18 changed files
• Comments generated: 4
• Review effort level: Medium