fix(compiler): cap rendered diagnostics to avoid RangeError on large reports

[techfreaque]

Problem

On a program with a very large number of diagnostics (thousands), the scriptc coverage command crashes outright instead of printing a report:

file:///.../packages/compiler/dist/coverage/report.js:217
    return out.join("\n");
               ^
RangeError: Invalid string length
    at Array.join (<anonymous>)
    at renderCoverage (.../coverage/report.js:217:16)

Root cause

The crash surfaces in renderCoverage, but the actual cause is one level deeper: renderAll() in packages/compiler/src/diagnostics/render.ts renders every diagnostic — each carrying its own source-line context snippet — and joins them all into one string with no size limit. With enough diagnostics, the joined string exceeds V8's maximum string length, and the whole report crashes with an uncatchable-feeling RangeError instead of showing the user anything at all, including the diagnostics that would have fit.

renderCoverage's own out.join("\n") calls are bounded by report sections and grouped/deduplicated blockers, not raw diagnostic count, so they aren't a second unbounded site — the fix belongs entirely in renderAll.

Fix

Cap renderAll at 1000 rendered diagnostics (sorted, so the same diagnostics render first every time) and append a note stating how many were omitted and the true total, instead of silently truncating or crashing.

Verification

• packages/compiler: tsc -p tsconfig.json — 0 errors.
• tests/harness/coverage.test.ts (which exercises renderCoverage, including the code path that calls renderAll) — all tests pass.
• tests/harness/diagnostics.test.ts (which exercises renderAll directly against a corpus of diagnostic-producing programs) — ran clean on the modified render logic; unrelated to this change, this suite currently has pre-existing snapshot path-normalization failures in this environment that reproduce identically on main.

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