fix(grok): include subagent session usage

[robinebers]

TL;DR

Include Grok subagent, resumed, and forked session usage in local spend tiles and Usage Trend, while retaining event-ID/model deduplication. Fixes #1191.

What was happening

• The scanner skipped every session marked subagent*, assuming the coordinator already included its usage.
• Child work missing from coordinator turns disappeared from spend totals and could leave entire days without usage.
• An unreadable session summary also excluded an otherwise valid usage ledger.

What this changes

• Scan every durable updates.jsonl ledger regardless of session kind, without requiring summary.json.
• Preserve existing event-ID/model deduplication across parent and child logs.
• Add regression coverage for child-only days, subagent/resume/fork sessions, replayed multi-model events, and malformed summaries.
• Update the Grok provider documentation to describe child-session accounting.

Heads-up

• Deduplication uses event IDs and models, not matching token totals: separate turns can have identical totals.
• Weekly billing metrics and metric layout defaults are unchanged.

Tests

• swift test --filter Grok compiled successfully; the local Xcode beta test runner initially could not locate Sparkle.
• After linking the existing Sparkle artifact into the local build's PackageFrameworks directory, swift test --skip-build --filter Grok passed all 50 tests.
• CONFIG=debug ./script/build_and_run.sh verify rebuilt, signed, and launched the dev app successfully.
• git diff --check passed.

---

Note

Medium Risk
Changes Grok spend aggregation logic users rely on for cost visibility; dedup by event ID may miss edge cases where IDs differ for the same work.

Overview
Grok local spend tiles no longer exclude subagent, fork, and resume sessions based on summary.json session_kind. The scanner now ingests every updates.jsonl under $GROK_HOME/sessions, so usage that only appears in child ledgers shows up in Today / Yesterday / Last 30 Days.

Double-counting is still avoided by the existing event ID + model dedup when the same turn_completed is copied across parent and child logs. Sessions with missing or malformed summary.json are counted again instead of being dropped entirely.

Tests and Grok provider docs were updated for child-only days, replayed events, and summary-independent reads.

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