Mock provider: diagnostics not sorted by range.start (spec §9.2 MUST) #68

Audit finding M1 — verified live.

Problem

methods.rs:94,119 emit parsed.diagnostics verbatim. parse.rs pushes diagnostics in phases — body-loop syntax errors first, then missing-section at puzzle.name_range (line ~0), duplicate-op, unresolved-op, warnings — so a document with a late syntax error and a missing section emits [error@line5, missing-section@line0]. §9.2: "Diagnostics within an entry MUST be sorted by range.start."

Reproduction

lpp/check on "puzzle p {\n start = 1\n ops {\n d: x => x + 1\n }\n solution = [ d ]\n ???\n}" — the ??? error at line 5 precedes the missing-target diagnostic at line 0.

Acceptance criteria

• diagnostics arrays emitted by lpp/check and lpp/compile are sorted by range.start (stable within equal positions).
• Regression test + green suite.