techniques: ctx.add_cost is per-step (ContextVar) — no more lost or double-counted dollars under gather - #38
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techniques: ctx.add_cost is per-step (ContextVar) — no more lost or double-counted dollars under gather#38ChrisW09 wants to merge 1 commit into
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_manual_cost was plain instance state shared by every step: a compose that gathers two ctx.run calls had stage B's reset wipe stage A's accrued dollars, and both steps read the same residual — costs vanished or were double-counted (verified: $0.11 of add_cost reported as $0.02). A compose-body add_cost was likewise wiped by the next ctx.run's reset, or dropped entirely after the last one. The manual-cost sink is now a ContextVar set around each technique call — the same isolation pattern the LLM usage sink already uses, so gathered steps (tasks copy their context) each accrue their own costs. add_cost outside any step charges the run's total_cost directly instead of being dropped. Fixes #12 Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Fixes #12.
Context._manual_costwas shared instance state, reset at the start of everyctx.runand read at the end — so overlapping steps corrupted each other. Verified failures:asyncio.gather(ctx.run("ret_a"), ctx.run("ret_b"))where A adds $0.10 and B adds $0.01 reported a total of $0.02 (A's dollars vanished, B's double-attributed);ctx.add_costin the compose body was wiped by the next step's reset or dropped after the last one. The module docstring explicitly invites this control flow ("branches, cascades, loops — the topology is entirely yours").Fix: the manual-cost sink is now a
ContextVarset/reset around each technique call — the exact isolation patternllm._usage_sinkalready uses (asyncio tasks copy their context, so gathered steps get independent sinks; nestedctx.runrestores the outer sink on exit).add_costcalled outside any step (compose body) charges the run'stotal_costdirectly, so dollars are never silently dropped.Regression tests: concurrent-stages attribution (exact per-stage and total assertions) and compose-body accrual. The existing manual-cost test (
test_per_technique_and_manual_cost_flow_to_stage_report) passes unchanged.Test: full cafe-core suite — 112 passed (1 pre-existing failure = #4, fix in PR #34).
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