[dmitrii-f-t27]

Closes #1824

Adds docs/chat/T27_PORT_CONVENTIONS.md recording owner decisions D2, D4, D5 and the single convention every trios-chat spec/swap follows:

• spec location and module line
• text language
• the verdict (named struct, Ok first)
• types, bytes and constructs
• tests
• behaviour fidelity
• checks before a PR
• swap layout
• crypto boundary
• words we do not use
• toolchain traps

Every .t27 snippet in the doc was verified:

t27c test-report -> 6 pass, 0 FAIL, 0 vacuous
t27c coverage -> Untested: 0
t27c gen-rust + rustc --edition 2021 --crate-type lib -> compile OK

t27c built from Trinity-S-AI-DNA/t27@4df8f0a

No CODEOWNERS changes.

[tri-claw]

Summary by t27-bees

This PR adds a comprehensive conventions document (docs/chat/T27_PORT_CONVENTIONS.md) that codifies owner decisions (D2, D4, D5) and the single porting convention for all trios-chat specs and swaps. It covers spec location, t27 language rules, the named-verdict struct pattern, allowed/disallowed constructs, test requirements, behaviour fidelity, pre-PR checks, swap order, crypto boundary, forbidden words, and toolchain traps.

Worth a look

• Line 68–76 (verdict struct): ExtVerdict carries all payload fields (claimed, actual, leaf, sender, joining, ops, ops_len) for every error variant, but most variants only need a subset (e.g., EpochMismatch only uses claimed/actual). This wastes space and leaves fields effectively uninitialized for irrelevant variants — the generated Rust may contain garbage or require manual zeroing.
• Line 133 (rustc command): rustc --edition 2021 --crate-type lib --out-dir out out.rs uses out as both the output directory and the input file basename (out.rs). This works but is confusing; a clearer example would separate names (e.g., --out-dir gen gen.rs).
• Line 107–120 (test examples): Tests call check_external_commit with many arguments, but the function signature is not specified in the conventions. Without a prescribed signature, reviewers cannot verify that test calls match the actual gate function.
• Line 44 (module second line): States “The second line is a use of any shared module” but the example on line 43 shows only the module line. A concrete use example would prevent ambiguity.
• Line 76 (verdict struct fields): No guidance on what values the unused payload fields should hold for a given error variant (zero? undefined? omitted?). The generated Rust must initialize all struct fields; the convention should state the rule.

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