feat(web): /calc expression evaluator -- pipeline-ab card 2 Arm B (STREAMLINED)

[eksno]

EXPERIMENT PR (card 2: harder, separating) -- DO NOT MERGE. pipeline-ab Arm B (STREAMLINED).

Streamlined lean layout: Composer 2.5 hands + review-reconcile only.

Correctness-deep card (expression parser/evaluator) chosen to separate Composer-hands-vs-Opus-hands. Both arms build from ONE shared plan. Stays OPEN for eyeball evaluation against its live Railway preview.

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[railway-app]

🚅 Deployed to the testing-pr-12 environment in testing

Service	Status	Web	Updated (UTC)
testing	✅ Success (View Logs)	Web	Jun 12, 2026 at 8:31 pm

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 77647d6d-7eec-4135-bb5f-9f46d1bac72c

📥 Commits

Reviewing files that changed from the base of the PR and between c20b967 and 6ea4095.

⛔ Files ignored due to path filters (1)

• web/package-lock.json is excluded by !**/package-lock.json

📒 Files selected for processing (24)

• web/package.json
• web/src/lib/calc/calculate.test.ts
• web/src/lib/calc/calculate.ts
• web/src/lib/calc/evaluate.test.ts
• web/src/lib/calc/evaluate.ts
• web/src/lib/calc/format.test.ts
• web/src/lib/calc/format.ts
• web/src/lib/calc/index.ts
• web/src/lib/calc/parse.test.ts
• web/src/lib/calc/parse.ts
• web/src/lib/calc/tokenize.test.ts
• web/src/lib/calc/tokenize.ts
• web/src/lib/calc/types.ts
• web/src/lib/clipboard.test.ts
• web/src/lib/clipboard.ts
• web/src/lib/components/site-header.svelte
• web/src/lib/components/toaster.svelte
• web/src/lib/toast-core.test.ts
• web/src/lib/toast-core.ts
• web/src/lib/toast.svelte.ts
• web/src/routes/+layout.svelte
• web/src/routes/calc/+page.svelte
• web/src/routes/calc/+page.ts
• web/vitest.config.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/calc-arm-b

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[eksno]

Final review (advisory -- not a merge gate)

/calc Arm B (lean, Composer-authored / Opus-gated) -- review report

ONLY review gate. Advisory; never blocks ship. Whole-diff red-team across three
lenses (spec / standards / quality). Change = git diff origin/alpha...HEAD
(commit 6ea4095). 25 files, +1833. Tests/check/build reported green by the
upstream gate; independently re-confirmed npm run test (89 passed / 7 files).

Verdict

Core is correct and spec-faithful. Every grammar/precedence/associativity rule,
the full error taxonomy, the divide-by-zero gate, the non-finite gate, and the
12-sig-digit float formatting match the plan verbatim. The required 7-file test
floor exists and every Section-6 case is present and passing. SSR/prerender
safety, theme-token-only styling, and the toast timer-leak cleanup are all in
place. ONE advisory finding: a pre-existing repo eslint config gap makes
npm run lint fail on the first .svelte.ts file. Out of allowed scope to fix
(eslint.config.js is DO-NOT-TOUCH); does not affect check/build/test.

Lens 1 -- spec gaps

No correctness gaps.

• Grammar (parse.ts): precedence-climbing exactly per plan. ^ right-assoc
  (RHS recurses into parseUnary) -> 2^3^2 AST is ^(2, ^(3,2)). Unary minus
  looser than ^ (parseUnary wraps parsePower) -> -2^2 AST is
  unary(-, ^(2,2)). 2^-2 valid via RHS-through-unary. All asserted.
• Error taxonomy: traced every disambiguation case by hand and all match --
  2+/2* -> Incomplete; (2+3 -> Mismatched; 2)+3/2 3/2(3)/2**3
  -> Unexpected token; () -> Incomplete (not Mismatched); 1/0/0/0/5/(2-2)
  -> Division by zero; 1e308*10 -> Result is not a finite number; bare ./1e
  -> Unexpected character with the exact offending char. Strings copied verbatim.
• format.ts: -0/0 -> '0'; round via Number(n.toPrecision(12)); exp branch on
  abs >= 1e21 || abs < 1e-6 with mantissa trailing-zero trim. 1e21->'1e+21',
  0.0000005->'5e-7', 0.1+0.2->'0.3', 1/3->'0.333333333333' all verified.
• calculate.ts: empty/whitespace pre-check; single try/catch; CalcError ->
  message, anything else -> 'Invalid expression'; non-finite gate post-eval.
• UI (+page.svelte): live $derived(calculate(...)), empty state muted (not
  red), error in text-destructive + aria-invalid, Enter/"=" commit, history
  most-recent-first capped at 10, per-row Copy -> toast. Matches Section 4.
  Minor: empty-state copy reuses "Enter an expression" rather than the plan's
  suggested "Type an expression above" -- but Section 9 item 9 explicitly says
  render the Enter an expression state as the neutral empty state, so this is
  compliant, not a gap.
• Nav + layout: /calc added to nav array; <Toaster/> mounted once in
  +layout.svelte after footer. Per manifest.
• Deps: only vitest + jsdom added; test/test:watch scripts + vitest.config.ts
  present. No parser library. tsconfig/eslint/prettier/svelte.config untouched.

Lens 2 -- standards

• Svelte 5 runes throughout: $state, $derived, $props, $effect. Toast
  store correctly carries .svelte.ts (module-scope $state); timer logic
  split into plain toast-core.ts for node-testability, per plan Section 5.2.
• Intra-$lib imports use .js/index.js extensions as the repo does. $lib
  alias used in source and re-aliased in vitest.config.ts.
• Prettier: npm run prettier --check passes for all files (tabs, single
  quotes, semis, es5 trailing comma).
• ASCII: -- used as the em-dash convention in copy and comments. No unicode.
• cn(): page uses inline class strings / array class syntax; cn() not required
  where no conditional class merge is needed -- consistent with existing pages.

Lens 3 -- quality

• PARSER CORRECTNESS: clean. Precedence, right-assoc ^, unary-minus binding,
  unary-in-exponent, no-implicit-mult, div-by-zero in evaluate, non-finite gate
  in calculate, 12-sig-digit formatting -- all correct and test-covered (89
  assertions). No dead branches; the parsePrimary op-vs-rparen split produces
  the exact taxonomy strings.
• Theme: toaster + page use only theme tokens (bg-card, text-destructive,
  text-muted-foreground, border-border, etc.). No hardcoded hex/rgb.
• Timer/subscription leaks: toaster $effect returns () => clearAllToastTimers();
  toast-core clearAll clearTimeouts every handle and empties the map; proven
  by toast-core.test.ts (clearAll -> cb never fires; pending() returns to 0).
• SSR/prerender: calculate('') is pure; no window/document/navigator at module
  scope or during render; clipboard.ts guards typeof navigator === 'undefined'
  and missing .clipboard. +page.ts restates prerender = true. Safe.
• Dead code: none. evaluate's nested switch is exhaustive; outer switch returns
  on every ast.type so check is satisfied.
• ESLint .svelte.ts gap (the flagged probe): npm run lint FAILS with
  Parsing error: Unexpected token interface on src/lib/toast.svelte.ts:3.
  Root cause: eslint.config.js applies tseslint.parser only via a
  files: ['**/*.svelte'] block; there is NO **/*.svelte.ts block, so the
  first .svelte.ts file in the repo falls through to espree (plain JS) which
  cannot parse interface. This is a PRE-EXISTING config limitation (the config
  pre-dates this branch and is in the plan's DO-NOT-TOUCH list), surfaced -- not
  introduced -- by this arm. The arm's file is correct: the plan MANDATES the
  .svelte.ts extension for the runes store, and interface Toast {} is normal
  TS. Fix belongs in eslint.config.js (add a files: ['**/*.svelte.ts'] block
  with parserOptions.parser = tseslint.parser), which is out of this arm's
  allowed scope. check/build/test are unaffected and green.

Gate evidence

• npm run test: 7 files / 89 tests passed.
• npm run lint: prettier clean; eslint fails ONLY on the pre-existing
  .svelte.ts parser gap (advisory).
• check/build: reported green by upstream gate; not re-run (no fix applied).

[eksno]

/calc Arm B -- triage disposition

Findings: 1. Acted-on: 0. Left: 1. Advisory gate -- never blocks ship.

ACTED-ON (applied in worktree)

(none -- the single finding is out of allowed scope to fix)

LEFT (judgement calls / out-of-scope)

1. npm run lint fails: Parsing error: Unexpected token interface at
   web/src/lib/toast.svelte.ts:3.
   • Reason left: PRE-EXISTING repo eslint config gap, not introduced by this
     arm. eslint.config.js has a files: ['**/*.svelte'] tseslint.parser block
     but none for **/*.svelte.ts, so the first .svelte.ts file falls through
     to espree and cannot parse TS interface. The proper fix edits
     eslint.config.js -- explicitly in the plan's DO-NOT-TOUCH list and outside
     this arm's allowed scope. The arm's file is correct (plan mandates the
     .svelte.ts extension; interface Toast is valid TS). check/build/test
     are green and unaffected; advisory only.

No-finding lenses

• Spec: no correctness gaps (one cosmetic copy note -- empty-state text reuses
  "Enter an expression" -- is plan-compliant per Section 9 item 9, NOT a finding).
• Standards: clean.
• Quality parser-correctness: clean.

Fix commits

none (no fix applied; nothing committed; nothing pushed).