Add the pi constant word

[thedavidmeister]

Adds a pi constant word, mirroring e (LibOpE). #535 rebased onto the split library: LibOpPi.sol, its registration in LibAllStandardOps between mul and power (ALL_STANDARD_OPS_LENGTH 72 -> 73, later word indices shift by one), and LibOpPi.t.sol.

The word reads LibDecimalFloat.FLOAT_PI from rain-math-float 0.2.1 (rain.math.float#274), exactly as e reads FLOAT_E. The library owns the constant and its checks: packLossless of the 67-digit coefficient at -66 in Solidity, and π by Machin's formula in Rust bound to the library source. Nothing about the value is restated here.

Stacked on #580 (the pin bump). Closes #225. Supersedes #535.

QA

• Discriminating tests: LibOpPi.t.sol parses _: pi(); and evals to LibDecimalFloat.FLOAT_PI, checks integrity (0 in, 1 out), the disallowed operand, and bad input / output arity; LibAllStandardOps.t.sol pins pi at word index 59 with every later word shifted. 14 tests across those suites pass over the new pins; the full suite is on Pin rain-math-float 0.2.1 and rain-math-float-deploy 0.1.2 #580.
• Mutations applied: run returning FLOAT_E instead of FLOAT_PI fails testOpPiRun against referenceFn; the registration is pinned by the word-order test (drop the pi entry and index 59 reads power).
• Oracle: the library's constant, whose value the library tests against Machin's formula and the packed decimal; this PR asserts the word pushes it.
• Category check: word for pi #225 asks for a pi word; delivered as the e word is built, with no value carried in rainlang.

🤖 Generated with Claude Code

https://claude.ai/code/session_01QyCCzi9WZPhuXcU1hwr2bq

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ℹ️ Recent review info

⚙️ Run configuration

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Run ID: 7650ae3c-6082-48f6-a61e-22ce39d1ff03

📥 Commits

Reviewing files that changed from the base of the PR and between 16c2d92 and 76753c3.

📒 Files selected for processing (4)

• src/lib/op/LibAllStandardOps.sol
• src/lib/op/math/LibOpPi.sol
• test/src/lib/op/LibAllStandardOps.t.sol
• test/src/lib/op/math/LibOpPi.t.sol

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📝 Walkthrough

Walkthrough

Adds the pi opcode with a fixed FLOAT_PI result, registers it among standard operations, and tests integrity, runtime evaluation, registry ordering, invalid input/output counts, and disallowed operands.

Changes

Pi opcode

Layer / File(s)	Summary
Implement and register pi src/lib/op/math/LibOpPi.sol, src/lib/op/LibAllStandardOps.sol	Defines FLOAT_PI, a zero-input and one-output integrity contract, stack execution, and a reference function. Registers the opcode and increases the standard opcode count to 73.
Validate pi behavior test/src/lib/op/math/LibOpPi.t.sol, test/src/lib/op/LibAllStandardOps.t.sol	Tests integrity, runtime output, evaluation, registry ordering, invalid input/output counts, and disallowed operands.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 76753

This adds a pi constant word that evaluates to the expected float value while rejecting invalid operands and arities. The implementation and registry behavior are covered, with no concrete current-head merge risk identified.

Sequence Diagram(s)

sequenceDiagram
  participant I_INTERPRETER
  participant LibAllStandardOps
  participant LibOpPi
  participant Stack
  I_INTERPRETER->>LibAllStandardOps: resolve pi opcode
  LibAllStandardOps->>LibOpPi: execute registered run function
  LibOpPi->>Stack: push FLOAT_PI

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The pull request implements the pi constant word requested by issue [#225]. It adds the opcode, registers it in the standard operation registry, and adds integrity, runtime, parsing, and ordering test…
Out of Scope Changes check	✅ Passed	All changes support the pi constant word objective in [#225]. The implementation, registry update, and tests are in scope. No unrelated deployment or generated-file changes are present.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding the pi constant word.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 2026-09-07-pi-word

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[thedavidmeister]

Draft until FLOAT_PI lands in rain.math.float beside FLOAT_E and this repo's rain-math-float pin moves to that release; then LibOpPi reads LibDecimalFloat.FLOAT_PI exactly as LibOpE reads FLOAT_E, and the local literal goes.

[github-actions]

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