Review P5-8: common-control wndproc split

2026-09-19: split the 9,327-line src/09c3-wndprocs.wat at existing top-level section boundaries. Function/data order and all function bodies are preserved; only a blank separator line differs in the concatenation.

src/main.watx remains the sole include-order authority. The sole affected region owner, $edit_layout_len, now names the Edit fragment; no region extent, address, or generated mirror changes. CLAUDE's source map and the basic-controls cross-reference are updated. This is an organization change, not a control-behavior fix. Other oversized files, including 09a handlers, OLE and DirectX, remain; the broad review split item is not fully closed.

Verification

• Concatenated source matches the original after ignoring blank-line runs.
• Compile the complete current source twice: once with the original monolith injected at its old position and the five new bodies empty, once normally. Complete WASM buffers are byte-identical in both tail-call and compatibility modes (1,441,967 and 1,442,873 bytes in that snapshot). This checks function indices and data ordering, not only module validity.
• Full bash tools/build.sh passes all gates and both builds, including owner attribution, manifest ordering, control variants and data overlaps. Another agent is editing Win16 in this shared tree; the independent full build's sizes differ from the paired-compile snapshot, so they are not presented as the same artifacts.
• Toolbar width, parent/child paint, property-sheet page lifetimes and Unicode Edit text regressions pass.

Local evidence: /private/tmp/wa-control-fragment-equivalence.log, wa-control-fragment-build.log, wa-control-split-toolbar.log, wa-control-split-paint.log, wa-control-split-page-handles.log, wa-control-split-edit.log.