feat(usage): separate auxiliary model calls from a Session's cost and cache hit rate

[liugddx]

Problem

A Session's usage figures in Desktop mix the main agent loop with every auxiliary model call made for that Session, and there is no way to separate them.

• Auxiliary calls pass telemetrySessionId: sessionId to runHostAuxiliaryModelCall. These are Session title, recap, goal evaluation, memory extraction, WorkHub intent/recall, and next-prompt suggestions once feat(desktop): add opt-in next prompt suggestions #5629 lands.
• The Session Inspector loads usage:summary with { range: 'all', sessionId } (apps/desktop/src/preload/preload.ts:1367). That summary feeds both estimatedSessionCost and usageCacheHitRate (session-inspector-overview-model.ts:194, :245-254, computed as cacheRead / input).
• UsageQuery (packages/core/src/usage-stats/types.ts:42-50) can filter by session, connection, provider, model, tool and status, but not by callKind. Consumers therefore cannot exclude auxiliary calls, and cannot break a Session's cost down by kind.

Until now this mattered little, because most auxiliary calls run once or rarely per Session. A per-reply auxiliary call such as #5629 changes that:

• Cost. Every reply adds an extra call that the user sees as Session cost, with no way to tell it apart from the agent's work.
• Cache hit rate. Auxiliary prompts do not share the main loop's cached prefix. Example: a main turn of 100k input tokens at 95% cache reads, plus one uncached 10k-token suggestion call, moves the displayed rate from 95% to about 86%. The main loop's caching did not change at all.
• Daily Review. Its request counts are inflated in the same way.

A second, smaller accuracy gap is on the failure path of runHostAuxiliaryModelCall (execution-model-authority.ts:691-701). When a call is aborted or fails, it is recorded with inputTokens: 0, outputTokens: 0, even though the provider may already have processed, and billed, the request. For example, a reasoning call aborted by a short deadline could have been billed for its input plus any reasoning tokens.

Desired outcome

• Add a callKind (or callKinds / excludeCallKinds) filter to UsageQuery, so consumers can ask for the main loop only, or for a per-kind breakdown.
• Base the Session Inspector's cache hit rate on main calls only. Optionally show auxiliary spend as its own line next to the Session cost, instead of folding it in silently.
• Where the provider or SDK reports partial usage on abort or error, record it. If it can't be known, mark the row as usage-unknown rather than zero.

Alternatives or workarounds

• Auxiliary calls could omit telemetrySessionId, so they only appear in global usage. That hides them from the Session entirely, which is worse for cost transparency.
• feat(desktop): add opt-in next prompt suggestions #5629 could state in its copy that suggestion spend is counted in the Session's cost. That documents the mixing but does not fix the hit-rate distortion.

Found while reviewing #5629 (review: #5629 (review)).

AI disclosure: Claude Code (Claude Opus) traced the usage path at 276faf1c9 and drafted this issue; liugddx reviewed it and is the human contributor of record.

[ggbdpq]

take

[anbv29]

Hi! I’d like to verify which documentation snapshot is authoritative, reproduce the version/links problem, and propose a focused correction. Is there a preferred owning repository for the fix?