feat(telemetry): add diagnostic fields, GDPR annotations, and InvocationGuard infra

Telemetry contract changes to unblock per-tool quality analysis (driven by the 9-query deep-dive in debugagent/06-深度诊断-PR定向-2026-06-09.md):

1. GDPR annotation blocks (the root cause of PR #1644 fields being filtered)

   - Added /* __GDPR__ ... */ blocks above the three sanitizedSend call sites

     (recordToolInvocation, recordChatActivation, recordLaunchInternal) so the

     ddtelfiltered cluster keeps new Properties keys instead of stripping them.

2. Five new enums to replace stringly-typed fields:

   - OperatingSystem: win | mac | linux | other

   - ClassNameDetectionStrategy: mavenStandard | gradleStandard | vscodeSrc | workspaceRoot

   - ClassNameDetectionFailure: sourceDirMissing | fileNotFound | parseError | noPackageDeclaration

   - SentinelOutcome: recorded | silentReturn | cancelled | exception

3. ToolInvocationRecord extended with platform/version context:

   - os, javaMajorVersion, projectSystem, retryCount, previousOutcome

   These split the per-tool funnel by OS / Java major / project system so we can

   confirm the Linux 4.3 percent vs Windows 27.7 percent start-rate divergence.

4. LaunchInternalEvent union extended with four new sentinel variants and elapsedMs/thresholdMs:

   - debugSession.sentinel: emitted on EVERY invoke so even infinite hangs leave a trail

   - debugSession.silentReturn: invoke returned with no outcome event (the 32.8 percent gap)

   - debugSession.cancelled: user cancelled mid-flight

   - debugSession.exception: handler threw an exception, classified

   - classNameDetection.failed: replaces collapsed boolean with strategy + failureReason

   - debugSessionStarted/Timeout now carry elapsedMs + thresholdMs for histograms

5. InvocationGuard infrastructure (beginDebugSessionInvocation()):

   - Returns markOutcomeRecorded / markException / close methods

   - Emits sentinel at begin; close auto-emits silentReturn if no outcome recorded

   - Lets us measure the 32.8 percent silent-loss bucket with closed-loop attribution

6. SessionInvocationTracker (nextAttempt / completeAttempt):

   - Per-window, per-tool in-memory retry counter

   - Stores ONLY enum (previousOutcome) and integer (count) — no user data

   - Quantifies the LM auto-retry-pays-off pattern (17.7 percent at 1 -> 64.9 percent at 6-10)

Compiles clean (tsc --noEmit) and passes tslint.

Author: Copilot CLI