feat: add mpairs m builtin (map→[k v] iteration)

[danieljohnmorris]

Summary

• Adds mpairs m > L (L _) builtin: takes a Map, returns a sorted-by-key list of [k, v] 2-element lists
• Satisfies invariant mpairs m == zip (mkeys m) (mvals m) with a single-walk native opcode (not a desugar)
• Wired through: builtins.rs enum + name lookup, interpreter/mod.rs #[inline(never)] dispatch helper, verify.rs signature M t a > L L _, vm/mod.rs tree-bridge eligibility, examples/mpairs.ilo, tests/regression_mpairs.rs (7 tests), SPEC.md + ai.txt

Closes ILO-43.

Test plan

• cargo test --test regression_mpairs — 7 tests, all pass
• Basic shape: text-keyed map returns sorted [k, v] pairs
• Invariant: output matches zip (mkeys m) (mvals m) form
• Empty map returns []
• Single entry returns [[k, v]]
• Numeric keys sort numerically (2 < 5 < 10, not lexicographic)
• After mdel: removed key absent from pairs

🤖 Generated with Claude Code

[codecov]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
4841	2	4839	0

View the top 2 failed test(s) by shortest run time

ilo::examples::examples

Stack Traces | 9.18s run time

thread 'examples' (44185) panicked at tests/examples.rs:158:9:
4/1242 example test(s) failed:

mpairs.ilo (line 19): `ilo .../ilo/examples/mpairs.ilo pairs`
  FAILED (exit exit status: 1)
  stderr: {"code":"ILO-P003","labels":[{"col":11,"end":662,"line":17,"message":"here","primary":true,"start":661}],"message":"expected `)`, got `:`","notes":[],"severity":"error"}

mpairs.ilo (line 21): `ilo .../ilo/examples/mpairs.ilo empty`
  FAILED (exit exit status: 1)
  stderr: {"code":"ILO-P003","labels":[{"col":11,"end":662,"line":17,"message":"here","primary":true,"start":661}],"message":"expected `)`, got `:`","notes":[],"severity":"error"}

mpairs.ilo (line 23): `ilo .../ilo/examples/mpairs.ilo nums`
  FAILED (exit exit status: 1)
  stderr: {"code":"ILO-P003","labels":[{"col":11,"end":662,"line":17,"message":"here","primary":true,"start":661}],"message":"expected `)`, got `:`","notes":[],"severity":"error"}

mpairs.ilo (line 25): `ilo .../ilo/examples/mpairs.ilo iter`
  FAILED (exit exit status: 1)
  stderr: {"code":"ILO-P003","labels":[{"col":11,"end":662,"line":17,"message":"here","primary":true,"start":661}],"message":"expected `)`, got `:`","notes":[],"severity":"error"}
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

ilo::examples_engines::examples_all_engines

Stack Traces | 9.28s run time

thread 'examples_all_engines' (44189) panicked at tests/examples_engines.rs:235:9:
4/1228 multi-engine example test(s) failed:

mpairs.ilo [vm] (line 19): `ilo .../ilo/examples/mpairs.ilo --vm pairs`
  FAILED (exit exit status: 1)
  stderr: {"code":"ILO-P003","labels":[{"col":11,"end":662,"line":17,"message":"here","primary":true,"start":661}],"message":"expected `)`, got `:`","notes":[],"severity":"error"}

mpairs.ilo [vm] (line 21): `ilo .../ilo/examples/mpairs.ilo --vm empty`
  FAILED (exit exit status: 1)
  stderr: {"code":"ILO-P003","labels":[{"col":11,"end":662,"line":17,"message":"here","primary":true,"start":661}],"message":"expected `)`, got `:`","notes":[],"severity":"error"}

mpairs.ilo [vm] (line 23): `ilo .../ilo/examples/mpairs.ilo --vm nums`
  FAILED (exit exit status: 1)
  stderr: {"code":"ILO-P003","labels":[{"col":11,"end":662,"line":17,"message":"here","primary":true,"start":661}],"message":"expected `)`, got `:`","notes":[],"severity":"error"}

mpairs.ilo [vm] (line 25): `ilo .../ilo/examples/mpairs.ilo --vm iter`
  FAILED (exit exit status: 1)
  stderr: {"code":"ILO-P003","labels":[{"col":11,"end":662,"line":17,"message":"here","primary":true,"start":661}],"message":"expected `)`, got `:`","notes":[],"severity":"error"}
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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