T01: cost-accounting survey — and a 2.7x correction to our own numbers

Tier L (structural L, chaos d10=2). Every candidate exercised locally
against the CB-WP-0001 transcript rather than cited.

Verdict: session transcript JSONL is the only exact instrument; git
commits supply the attribution index it lacks; the State Hub is a
durable sink whose schema cannot express cache tokens at all; the
status bar and billing API are eliminated on availability.

Three errors found in this workplan's own Purpose section, all
overstating cost:

  - one API response is written as up to six JSONL lines, each
    repeating the same usage object (657 lines, 346 responses)
  - a multi-model session was priced entirely at Fable 5 rates,
    violating a per-model rule MetricsAndScenarios §1a already had
  - the transcript is a live file, so an unpinned total is not
    repeatable (346 -> 356 responses between two runs minutes apart)

CB-WP-0001 pinned at fc76445: $92.21, not $248.46. The qualitative
finding sharpens rather than weakens — 88.4% of spend is cache, at
256:1 cache-read to output tokens.

Neither error was of the harness-does-nothing class the positive
control was written for; both sums ran over real data. What caught
them was re-deriving a number instead of quoting it. Raised for T07
and for CB-WP-0003 T01.

Also measured: the one subagent (adversarial review) cost $0.66 and is
invisible to a collector reading only the main transcript.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

history/260731-cost-accounting-research.md

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+# 2026-07-31 — how the cost-accounting survey was conducted
+
+Trail for `research/CB-RES-0002-cost-accounting.md` (CB-WP-0002 T01).
+Tier L, chaos d10 = 2 (no override).
+
+## Method
+
+No web sources. Every candidate was exercised locally against the
+CB-WP-0001 session transcript
+(`~/.claude/projects/-home-worsch-clay-borg/8cbd5701-….jsonl`, 5.1 MB,
+2,040 lines) and the clay-borg git history. The survey's own rule —
+measured beats cited — applied to itself, which is the only reason the
+errors below were found.
+
+## What was measured, in order
+
+1. **Transcript shape.** Counted line types and collected the union of
+   `usage` keys. Found 654 usage-bearing assistant lines, and four
+   distinct `message.model` values where one was assumed.
+2. **`usage.iterations`.** Suspected as a double-count source. Checked
+   whether iteration outputs sum to the top-level `output_tokens`: they
+   match in all 654 cases, and no message had >1 iteration. Cleared.
+3. **`requestId` cardinality.** 346 distinct ids across 657 lines. This
+   was the finding that overturned the workplan's numbers.
+4. **Dedup validation.** For all 208 multi-line groups, compared the
+   serialized `usage` object across the group: 208 identical, 0
+   differing, 0 mixed-model. Block-type patterns confirmed the split is
+   `thinking` / `text` / `tool_use`, i.e. a transcript-writer artifact.
+5. **Re-priced three ways** (per-line all-Fable, per-line per-model,
+   deduped per-model) to isolate how much of the error came from each
+   mistake: $289.12 / $210.05 / $93.15.
+6. **Hub API.** Called `get_token_summary` on CB-WP-0001's workplan.
+   401,100 tokens over 7 events for 9 tasks, all filed under Fable 5.
+   Compared against the transcript to quantify the gap (~8× on output).
+7. **Status bar and billing API.** Checked `~/.claude/settings.json` for
+   `statusLine` (absent) and for an admin key (absent). Both eliminated
+   on availability before any further evaluation.
+8. **Git boundaries.** Read `git log` with ISO timestamps to confirm
+   commit density and that subjects name tasks. Noted the UTC/+02:00
+   mismatch against transcript timestamps.
+9. **Subagent tree.** Found `<session>/subagents/` while checking whether
+   `isSidechain` was ever true (it never is). Priced the one subagent
+   transcript: $0.66.
+
+## Dead ends
+
+- **`isSidechain` as the subagent signal.** It is present on every line
+  and `false` on every line in this session; it does not mark subagent
+  work in the main file because subagent work is not *in* the main file.
+  Looking for a flag wasted a step that a directory listing answered.
+- **`tool-results/` sidecar directory** (340 KB) was inspected as a
+  possible cost source. It holds raw tool outputs for replay, carries no
+  usage data, and is not billed separately. Not a candidate.
+
+## The finding worth carrying forward
+
+The workplan that exists to make cost measurable **opened with a
+mismeasured cost**, off by ~2.7×, and its two errors were of different
+kinds: a format artifact (double-counted lines) and a rule that existed
+but was not applied (per-model pricing, already mandated by
+`specs/MetricsAndScenarios.md` §1a).
+
+The second is the more uncomfortable one. InnerLoop v1.0's answer to bad
+numbers is the positive control, and a positive control would not have
+caught either of these — both sums were over real data that really
+existed. What caught them was **re-deriving a number instead of quoting
+it**. That belongs in the loop as its own rule, and is raised for T07:
+*a number inherited from a previous pass is re-derived before it is used
+as a target, or it is cited as unverified.*
+
+Reported into CB-WP-0003 T01's rule-enforceability audit as well: this is
+a fifth error instance, and it is **not** of the harness-does-nothing
+class that T10 predicted. The class is "trusted arithmetic over real
+data".