[bercedev]

What & why

Closes #583

Screen::parse allocated cols × rows cells from the header before reading any grid line, and the header was only checked for zero. A 31-byte file declaring 65535x65535 aborted on a 206 GB allocation.

• parse_header (screen/parse.rs) now refuses a dimension above MAX_DIMENSION with Error::Parse. For example: line 1: 65535x65535 is past the 1000-per-axis limit of a terminal, so no termlens wrote this screen.
• It reuses the terminal's own constant, now pub(crate) in terminal.rs with its value and doc comment unchanged, so the two limits can't drift apart.
• The JSON reader (screen/serde_impl.rs) applies the same limit, before the row and cell counts are compared.
• A 1000x1000 screen still parses.

I left the optional repeated-span-lines part of the issue out to keep this to one change.

Tests (tests/compat.rs):

• a_declared_size_past_the_terminal_limit_is_refused_before_allocating: 65535x65535, 1001x1 and 1x1001 each give an Error::Parse naming the size and the limit, and 1000x1000 parses.
• json::a_json_size_past_the_terminal_limit_is_refused: a corpus plain.json with cols and rows set to 65535 is refused with the same message.

With the old parse.rs and serde_impl.rs, the compat test binary aborts with memory allocation of 206152138800 bytes failed (SIGABRT).

Checklist

• Linked an issue (or explained above why none exists)
• Tests added/updated for the change
• cargo fmt --all and cargo clippy --workspace --all-targets --all-features are clean
• All commits are signed off (git commit -s) — see CONTRIBUTING.md §5
• No AI attribution trailers (no AI co-authors, "Generated with" footers, or bot identities) — see CONTRIBUTING.md §6
• CHANGELOG.md updated under [Unreleased] (user-facing changes only)
• Snapshot changes (if any) were reviewed with cargo insta review, not blind-accepted (no snapshot changes)

Checked with Rust 1.99.1, offline:

• cargo test --workspace --all-features: 627 passed, 0 failed.
• cargo clippy -D warnings for the workspace with all features, and for -p termlens with default features, no default features, and decode only.
• cargo fmt --all --check.
• RUSTDOCFLAGS='-D warnings' cargo doc --no-deps --all-features.
• check-cli-contract.sh: PASS.
• check-dco.sh and check-no-ai-attribution.sh over main..HEAD.

This and #601 both add a ### Fixed section under [Unreleased]. Whichever lands second needs a one-line merge in CHANGELOG.md, and I'll rebase this one if it's second.

[vyncint]

Thanks — clean fix. Verified: the cap has held on the builder and on resize since 0.5.0, so no release STABILITY covers ever wrote a larger screen and the compat promise holds; compat tests pass locally, and the old code aborts on the new test as you said.