feat(copilot): track GitHub Copilot JetBrains IDE usage

[NihalJain]

What & why

The JetBrains Copilot plugin (IntelliJ, PyCharm, RubyMine, …) stores its chat/agent sessions under ~/.config/github-copilot/<ide>/<kind>/<storeId>/ — a location none of the existing Copilot sources (CLI JSONL, VS Code chat sessions/transcripts, OTel SQLite) read. As a result all JetBrains Copilot usage was silently uncounted in every CodeBurn report. This adds a reader for that store so those sessions are discovered, priced, and attributed to the right project.

Fixes #211

How it works

• Reader. The store's session content is a Nitrite .db — an H2 MVStore of Java-serialized documents. It is scanned as latin1 for byte-offset stability: no Java deserializer, no new dependency, and it is not SQLite so node:sqlite is not involved.
• Reply text. Assistant replies live in nested-escaped {"__first__":{"type":"Subgraph"…}} blobs. The text is recovered by unescaping one level at a time and, at the depth where the Markdown record's data field is a well-formed one-level-escaped JSON document, reading it structurally — so a reply containing its own quotes is never truncated or duplicated (which would otherwise inflate the estimate).
• Tokens/cost. The store records no token counts, so output tokens are estimated from the reply text (CHARS_PER_TOKEN = 4, re-decoded latin1→utf8 so multibyte replies count by codepoint) and every call is marked costIsEstimated. Failed generations (error status, no reply) are billed $0.
• Sessions. One .db holds many chat tabs; turns are grouped back to their conversation GUID so the UI shows one session per tab, deduped by reply content per conversation.
• Project attribution, most authoritative first:
  1. the plugin-recorded projectName field (JetBrains Copilot 1.12+), joined across kind dirs by store id — the billable turns live in chat-agent-sessions, but the label is usually written into the sibling chat-sessions/chat-edit-sessions store. Read length-delimited and re-decoded latin1→utf8 so non-ASCII repo names round-trip.
  2. the .git repo root of a referenced file:// path.
  3. a generic copilot-jetbrains bucket when neither signal exists. The conversation title is a chat-thread name, not a project, so it is kept out of the project field and surfaced as the session label instead.

Override the JetBrains github-copilot root with
CODEBURN_COPILOT_JETBRAINS_DIR.

Docs

• docs/providers/copilot.md — full JetBrains section (store layout, latin1 scan, reply extraction, projectName precedence + cross-kind join).
• docs/providers/README.md — Copilot storage updated to note the Nitrite .db.

How to verify

• npm test -- copilot and npx tsc --noEmit (fixtures reproduce the real nested-escaped .db framing, including quote- and multibyte-bearing replies).
• End to end against a real install: CODEBURN_CACHE_DIR=$(mktemp -d) node dist/cli.js status --provider copilot \ --period all --format menubar-json — JetBrains sessions appear By-Project under their real repo names.
• Set CODEBURN_COPILOT_JETBRAINS_DIR to a fixture root to parse a controlled store without touching the real config dir.

Summary

Testing

• I have tested this locally against real data (not just unit tests)
• npm test passes
• npm run build succeeds

For new providers only:

• I installed the tool and generated real sessions by using it
• npm run dev -- today shows correct costs and session counts for this provider
• npm run dev -- models --provider <name> shows correct model names and pricing
• Screenshot or terminal output attached below proving it works with real data

[NihalJain]

Screenshot (Before) with npx codeburn@0.9.15:

Screenshot (After) this patch:

[NihalJain]

@iamtoruk