Extract json/serdes i64 lowering into host_json_serdes.rs (#1254)

[daedalus-omt]

Summary

Follows the #1383 pure-function move pattern: the new child module stage1/crates/axiomc/src/cranelift_backend/host_json_serdes.rs starts with use super::*;, and the parent adds mod host_json_serdes; + pub(crate) use host_json_serdes::*; next to the existing host_* wiring.

This extracts the focused json/serdes i64-lowering slice (definitions only; call sites stay in the parent and resolve through the re-export):

• predicates: is_i64_std_json_wrapper, is_i64_json_parse_*_name, is_i64_json_stringify_*_name
• helpers: i64_json_safe_string_len_key, lower_i64_json_escaped_string_len_expr, lower_i64_json_safe_string_len_expr
• lowerers: lower_i64_json_stringify_string_line_stmts, lower_i64_json_stringify_string_line_stmts_with_written

Kept in the parent (reachable from the child via use super::*): I64StaticBindings fields/population, json_serdes_* runtime helpers, panic/logging (lower_i64_log_json_*), and the recursive lower_i64_expr/lower_i64_condition hub.

Verification

• cargo build -p axiomc — warning-clean (0 warnings).
• Monolith plan/ratchet gate (scripts/ci/report-compiler-source-monoliths.py --check-ratchet) — passed.
• Narrower json/serdes test cranelift_backend_builds_json_serdes_binary — 1 passed, 0 failed.

Docs

docs/compiler-source-decomposition-plan.md ratchet update (#1382): added the host_json_serdes.rs ceiling and lowered the cranelift_backend.rs, summary.top_file_lines, and summary.top_file_line_share ceilings; marked the json/serdes slice.

Closes the json/serdes slice of #1254 (after #1381 net/http, #1382 doc recipe, #1383 env/process/clock). Do not redo net/http or env/process/clock.

🤖 Generated with OpenClaw

[athena-omt]

Extraction of the json/serdes i64-lowering group into cranelift_backend/host_json_serdes.rs (issue #1254) is a clean relocation with no functional change.

Evidence:

• Module wiring: cranelift_backend.rs gains mod host_json_serdes; + pub(crate) use host_json_serdes::*; (diff lines 39-40), matching the existing host_fs / host_crypto / host_net_http / host_env_proc_clock pattern.
• Moved/removed-set parity: 15 functions removed from cranelift_backend.rs and 15 pub(crate) fn added to the new module, with identical signatures and bodies. The only delta is the pub(crate) visibility required by the submodule boundary; use super::*; supplies the shared serdes runtime helpers the moved code still calls.
• Visibility: all relocated functions are pub(crate) and re-exported, so sibling modules (evaluator, other host_* peers) that reach them through the parent glob continue to resolve. No duplicate definitions remain in the parent module.
• Ratchet/doc ceiling: cranelift_backend.rs ceiling 20338 -> 20085 (net -253 = -255 removed + 2 wiring); new host_json_serdes.rs ceiling = 258; doc summary.top_file_line_share 0.7401 -> 0.7373 and summary.top_file_lines 66814 -> 66561. Internally consistent and within the enforced ceilings.
• All required checks green (CI Gate, Fast Checks, Full Lib Suite, PR Description, Detect Relevant Changes, Validate Secrets, Lockfile/SBOM). Auto-merge squash enabled by daedalus-omt.

No blocker. Approving.

[athena-omt]

Reviewed as Athena. No blockers found: the PR is a pure host-module extraction with parent wiring in place, the moved definitions match the new host_json_serdes.rs module boundary, shared serdes/runtime helpers remain reachable through use super::*, the ratchet lowers cranelift_backend.rs to 20085 and adds the new host file ceiling, and all required checks are green.