feat(usage): report OpenCode spend and tokens from its local store

[jaikhuranna]

What changed

The Usage report covered Claude, Codex, and Grok Build but not OpenCode, so OpenCode-only users saw no spend or tokens. This adds OpenCode as a usage source following the same playbook the grok addition (v5) used:

• Contracts: UsageProviderKind gains "opencode". USAGE_CONTRACT_VERSION bumps to 6; USAGE_MERGE_COMPATIBLE_SINCE stays at 4 because the change is additive.
• Server: a new opencodeUsageStore.ts reads assistant rows from OpenCode's own SQLite store ($XDG_DATA_HOME/opencode/opencode.db, opened readOnly) through a pure parseOpenCodeMessage in usageTranscripts.ts. The store rides the existing (size, mtime) scan cache wholesale — there is no transcript byte stream to resume from.
• Normalization: OpenCode reports disjoint tokens (input excludes cache reads, output excludes reasoning), so reasoning folds into outputTokens per the contract's subset invariant; a zero reported cost falls through to the rate table, matching Claude Code subscription turns.
• Clients: one provider entry in web and mobile usage presentation (icon already existed).

Deliberately deferred to keep this thin: the per-thread context-window meter, cursor/antigravity sources, and reading session_message (v2 projection, empty in the wild; dedupeKey is the message id, so dual-reading later is additive-safe).

521 insertions across 14 files (~250 production, ~270 tests), verified with the touched suites: parser, store round-trip, one integrated service scan, scan-cache round-trip, and chart bands.

Worked by GLM (glm-flash-latest) via OpenCode.

[jaikhuranna]

Evidence: OpenCode usage on a real store

Both screenshots come from the same machine and the same opencode.db.

Before — the stable install's Usage page: $0.00, no activity. The user's history is entirely OpenCode sessions, which the usage contract ignored.

After — this branch: OpenCode appears with spend, tokens, cache savings, and a per-model breakdown, read from the same store (90-day window).

31 sessions · $30.27 · 254M tokens (231M cached input), cache savings $7.32. Models without rates (muse-spark-*, nvidia/nemotron) render as Unpriced and are excluded from cost totals.

[jaikhuranna]

Mobile verification

The phone app (T3 Code Dev, this branch, Android emulator) paired to a server running this branch. The Usage widget renders the OpenCode series from the v6 contract buckets with no provider-specific mobile code — it is driven entirely by the shared PROVIDER_ORDER, label, and color definitions:

OpenCode — $29.79 · 100.0% of cost · 245M tokens (90-day window), confirming the contract addition covers the mobile surface as-is.

[juliusmarminge]

Superseded by merged #10409, which added OpenCode (plus Cursor / Antigravity) usage history to the Usage page and resolved #6909. Closing this leftover PR — please reopen if it still covers something unique that #10409 missed.