Refactoring 3/35: Replace global state with parameter

[kryptt]

Entry 3 of the refactoring catalogue: Replace global state with parameter.

• Page at /refactorings/replace-global-state-with-parameter/ with the full entry shape: Motivation first, The move, To and from (koan), three Before/After example pairs in Scala 3 + Haskell, Pitfalls with the functional-reading footnote, Verification, 11 references.
• Every reference verified with a skeptic pass; the failures are recorded in LESSONS.md (Fowler bliki GlobalVariables.html/Singleton.html and refactoring.com/catalog/globalData.html are 404 — the smells are cited from the 2e book; Hevery's dead blog is cited via the Google Testing Blog post that quotes it; "State in Haskell" says state transformer, not "state-passing style").
• Examples: 01 a hidden setting (global constant becomes a leading parameter), 02 a shared policy record read by a fold step (whole record becomes one parameter; Haskell partial application at the fold), 03 a global mutable fresh-number supply (Scala var / Haskell top-level IORef) threaded as explicit state through a recursive walk — in Haskell the After entry point is pure again, and the signature records it.
• sh pages/refactorings/replace-global-state-with-parameter/run.sh ends with all properties passed.
• Skill memory updated in the same PR: LESSONS.md entry for this run + a withTests clarification in brief.md (it is a member of Test, not Property).
• .gitignore gains /vendor/ for bundle config set --local path vendor/bundle (system gem dir is not writable on this machine).

Mutation check (review round)

Example	Mutant	Language	Caught by
1	fee ignores its parameter, hard-codes 300	Scala, Haskell	purpose property (agreement passes)
1	fee applied twice	Scala	agreement property
2	< → <= at the overdraft boundary	Scala, Haskell	agreement, shrunk to List(-30) within 5 tests (500-test property)
2	limit hard-coded, parameter ignored	Scala	purpose property (agreement passes)
3	supply increments by 2 / never	Scala	both properties
3	right subtree numbered first	Haskell	label properties
3	forces the Lit payload	Haskell	laziness probe only

No mutant survived; wrong-typed mutants were not used.

Adversarial probes

• Haskell laziness: a Lit undefined payload survives the numbering in both versions; the mutant that forces it fails the probe.
• Evaluation order: labels come out exactly x0, x1, … in pre-order on generated trees (self-consistency oracle).
• Concurrency: example 3's Haskell spec uses checkSequential because the properties share Before's top-level IORef.

Verification

• bundle exec jekyll build exits 0.
• Headless-Chrome screenshots at 1280 and 390 wide: panes stack and scroll internally, no horizontal page scroll; diagrams render in dark (browser) and light (rsvg on white) — all SVGs are currentColor.

Preview: https://www.constructive.dev/pr-preview/pr-16/refactorings/replace-global-state-with-parameter/

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