SPEC: formalize trailing-; semantics (ILO-405)

[danieljohnmorris]

Summary

• Adds a Trailing-semicolon semantics section to SPEC.md (in the Functions chapter, after Inline lambdas) formalizing when ; is required, optional, or silently consumed
• Documents all three body contexts: top-level function bodies, inline-lambda bodies ((params>return;body)), and match/guard arm bodies
• Includes a table, practical rules, and a note on the one case that is an error (double-; at statement start)
• Adds tests/regression_trailing_semi.rs with 5 tests pinning the behavior

What was formalized

Context	Finding
Function body f>n;42;	Trailing ; silently consumed — identical to f>n;42
Inline lambda (x:n>n;+x 1;)	Trailing ; before ) silently consumed
Match arm ?x{1:10;_:20;}	Trailing ; before } silently consumed
Header separator name params>return;body	The ; separating the return type from the body is optional when a newline is present
Double-semicolon f>n;;42	Parse error — trailing-; consumption only applies after a valid statement

Test plan

• fn_body_trailing_semi_ignored — f>n;42 and f>n;42; both return 42
• fn_body_multi_stmt_trailing_semi_ignored — multi-statement body with trailing ; unchanged
• lambda_body_trailing_semi_ignored — (x:n>n;+x 1;) works in a map call
• match_arm_trailing_semi_ignored — ?x{1:10;_:20;} parses identically to without trailing ;
• double_semi_at_body_start_is_error — f>n;;42 fails with a parse error

Closes ILO-405.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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