Refactor to LET: rewrite a formula into a tidy LET

[jimmytacks]

Overview

New /Refactor slash command that takes the active cell's formula — LET or not — and rewrites it as a tidy LET where every cell ref and range appears as a single value binding. The author then runs /LET to LAMBDA as the next step. Mirrors the /Gather → /LET to LAMBDA two-stage pattern.

Worked example

Active cell:

=IF(A1<10, IF(A1>2, SUM(B1:B5), 0), SUM(B2:B6))

After /Refactor:

=LET(
    input1, A1,
    input2, B1:B5,
    input3, B2:B6,
    IF(input1<10, IF(input1>2, SUM(input2), 0), SUM(input3)))

Also handles the "messy LET" case: extracts refs from inside calculation bindings, merges duplicate value bindings (first name wins), and reorders inputs-before-steps.

Spec and plan

• Spec: specs/0008-refactor-to-let.md
• Plan: plans/0008-refactor-to-let.md

Implementation Plan

4 PR-sized slices, sequenced. PR 1 is a tracer bullet — end-to-end on non-LET formulas with cell refs / ranges / spill — so the feature is exercisable in Excel from day one.

• Refactor to LET — PR 1: tracer (non-LET formulas, refs + ranges + spill) #202 PR 1 — Tracer: non-LET formulas, refs + ranges + spill, end-to-end
• Refactor to LET — PR 2: existing-LET handling (full refactor) #203 PR 2 — Existing-LET handling (full refactor)
• Refactor to LET — PR 3: promotable named ranges + external refs #204 PR 3 — Promotable section: named ranges + external refs
• Refactor to LET — PR 4: promotable literals + drop-input UX polish #205 PR 4 — Promotable section: literals + drop-input UX polish