Amend CB-EV-0001; add CB-WP-0002 for cost accounting

AM-4: measured what each remediation option actually buys, rather than
leaving one recommendation unquantified. serde_yaml optional removes 6
crates, not 5 — ryu belongs to that group, since serde_json now uses
zmij for floats. Full ladder: -6 to 27, serde_json -4 more to 23,
inlining SHA-256 -8 to 19, inlining ChaCha12 -4 to 15. Only
reimplementing a primitive gets under 20, so the target is unreachable
without undoing K5/K7.

Also records that crate count compares badly across ecosystems, and
offers the alternative the count is a proxy for: 307,317 lines of
third-party source under audit against 3,398 of our own.

AM-12: corrected from "uncomputable" to measured. The refusal to
estimate was right; the claim that no instrument existed was wrong.
Session transcripts carry exact per-message usage including the cache
breakdown. This session cost $248.46 at Fable 5 rates, of which 53% is
cache reads — cost is driven by context size times turn count, not by
output volume. What is still missing is per-task attribution, since
nothing marks task boundaries in a transcript.

CB-WP-0002 makes cost measurable and attributable: survey the
instruments, decide the attribution model by ADR, spec metrics that
include cost composition rather than a bare total, build a collector
whose positive control refuses to emit unreconciled numbers, and prove
it by answering a question that could not be answered before.

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

.claude/ralph-loop.local.md

@@ -1,21 +0,0 @@
----
-active: true
-iteration: 3
-session_id: 8cbd5701-a096-45a4-a419-9b7b1c9419bc
-max_iterations: 20
-completion_promise: "HEUREKA"
-workplan_id: CB-WP-0001
-workplan_file: workplans/CB-WP-0001-inner-loop.md
-started_at: "2026-07-31T00:08:23Z"
----
-
-Read the workplan at `workplans/CB-WP-0001-inner-loop.md`.
-
-If every task has `status: done` AND frontmatter `status: done`:
-run `rm -f .claude/ralph-loop.local.md` first (deactivates the loop so the stop hook exits cleanly),
-then output <promise>HEUREKA</promise>.
-
-Otherwise implement the next `todo` task as described in the workplan.
-Set task `in_progress` when starting, `done` when complete.
-When all tasks are done set frontmatter `status: done`.
-