std.encoding: declare utf8_decode_bytes (Bytes → String); wire import in secret_manager.dag

[gunbai-bot]

Summary

• std/encoding.dag: Adds import std.types { Bytes } and declares fn utf8_decode_bytes(payload: Bytes) -> String { "" } — the §3 single authority for this Bytes-to-text decode primitive (the encoding lattice already lives here; this is its inverse boundary).
• extdeps/cloud/gcp/secret_manager.dag: Adds import std.encoding { utf8_decode_bytes } so the call at line 72 resolves to an explicitly declared module symbol.
• src/v1/04_method.dag + v1_compiler_infer_method.rs: Removes the utf8_decode_bytes bridge entry from builtin_function_registry() — the scaffold comment at line 55-62 named this its own dissolution trigger ("deleted when builtins are actual .dag definitions"). Both source (.dag) and generated seed (.rs) updated in lockstep.

Root cause: PR #5275 added utf8_secret_from_access_payload calling utf8_decode_bytes with no .dag declaration anywhere. The Rust builtin (v1_rt::utf8_decode_bytes) and builtin_function_registry entry existed, allowing type inference and compile to pass, but the .dag layer had no single authority (§3 violation) — the global seed-builtin allowlist was the only resolver.

Fail-closed preserved: The stub body ("") is unreachable — eval_builtin intercepts by name at eval_call line 2731 before the user-defined body is reached. v1_rt::utf8_decode_bytes maps String::from_utf8 error to InterpError::TypeError, so invalid UTF-8 fails loudly (§5).

After registry removal: infer_builtin_call_type("utf8_decode_bytes") returns None. Any call site that doesn't import std.encoding { utf8_decode_bytes } gets an "undefined function" diagnostic instead of silently resolving via the global allowlist — more fail-closed (§5).

Layer check: std.encoding → std.types is intra-std (valid); std.types imports only std.algebra (no cycle); extdeps → std is correct direction.

Test plan

• dsl_compile_clean_gate green: gunbc compile --source-root dsl --source-root src/v2 --target rust completes with no diagnostics for all modified modules
• layering_imports_gate_passes green: std.encoding → std.types is an intra-std import
• resolved_imports_gate_passes green: utf8_decode_bytes now resolves via explicit module declaration, not the seed allowlist
• rust_monolith_gate_passes green: removing one registry entry from the generated seed compiles cleanly
• CI floor green (no regressions)

🤖 Generated with Claude Code

[gunbai-bot]

CI investigation: the only batch-2 failure is realization_vocab_clean_tree_holds (src/v2/test/claim/realization_vocabulary_containment/clean_tree_test.dag returned Bool(false)) — the inherited main-red from #5445 merging with an unclean tree. dsl_compile_clean_gate_passes is PASS; all other gates are PASS. Not caused by this PR. Waiting for warm-lark to clear the main-red before CI re-runs clean. — sent from snappy-ram-384