fix(vm): resolve OP_SEED/OP_TAILCALL opcode collision

[danieljohnmorris]

Summary

PR #503 (seed builtin) and PR #518 (VM tail-call optimisation) both assigned opcode 189 in src/vm/mod.rs. OP_SEED is listed first in the dispatch match and silently shadows OP_TAILCALL, so VM tail-call dispatch has been broken on main since TCO landed.

The collision also produces a clippy unreachable_patterns warning. With -D warnings in CI that becomes an error, blocking every PR's lint check until this lands.

Fix

Renumber OP_SEED from 189 to 190 (next free opcode byte, verified by a grep -n "u8 = 19[0-9]" scan). OP_TAILCALL keeps 189 because it is on the hot dispatch path and has been wired up longer.

No call sites need updating - the opcode is referenced via the OP_SEED symbol in src/vm/compile_vm.rs, src/vm/jit_cranelift.rs, and src/vm/compile_cranelift.rs, so the constant change is enough.

Test plan

• cargo build --release --features cranelift clean
• cargo clippy --release --features cranelift --all-targets -- -D warnings clean (no more unreachable_patterns)
• cargo test --release --features cranelift --test regression_tco --test regression_tco_vm --test regression_rng_parity --test regression_rand_bytes all pass
• Full cargo test --release --features cranelift green except for one pre-existing failure in regression_reserved_names_doc::spec_reserved_short_names_match_builtin_registry, caused by the crypto-primitives PR that just landed adding b64/hex builtins without updating SPEC.md - unrelated to this fix

[codecov]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
4724	2	4722	0

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

ilo::examples::examples

Stack Traces | 7.07s run time

thread 'examples' (40491) panicked at tests/examples.rs:158:9:
9/1161 example test(s) failed:

crypto-primitives.ilo (line 42): `ilo .../ilo/examples/crypto-primitives.ilo sha-empty`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41115) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo (line 44): `ilo .../ilo/examples/crypto-primitives.ilo sha-abc`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41119) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo (line 46): `ilo .../ilo/examples/crypto-primitives.ilo hmac-rfc2`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41122) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo (line 48): `ilo .../ilo/examples/crypto-primitives.ilo b64-roundtrip`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41125) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo (line 50): `ilo .../ilo/examples/crypto-primitives.ilo b64-padded`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41128) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo (line 52): `ilo .../ilo/examples/crypto-primitives.ilo hex-abc`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41131) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo (line 54): `ilo .../ilo/examples/crypto-primitives.ilo ct-eq-yes`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41134) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo (line 56): `ilo .../ilo/examples/crypto-primitives.ilo ct-eq-no`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41137) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo (line 58): `ilo .../ilo/examples/crypto-primitives.ilo ct-eq-len`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41140) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

ilo::examples_engines::examples_all_engines

Stack Traces | 7.07s run time

thread 'examples_all_engines' (40492) panicked at tests/examples_engines.rs:235:9:
9/1147 multi-engine example test(s) failed:

crypto-primitives.ilo [vm] (line 42): `ilo .../ilo/examples/crypto-primitives.ilo --vm sha-empty`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41203) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo [vm] (line 44): `ilo .../ilo/examples/crypto-primitives.ilo --vm sha-abc`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41206) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo [vm] (line 46): `ilo .../ilo/examples/crypto-primitives.ilo --vm hmac-rfc2`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41210) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo [vm] (line 48): `ilo .../ilo/examples/crypto-primitives.ilo --vm b64-roundtrip`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41212) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo [vm] (line 50): `ilo .../ilo/examples/crypto-primitives.ilo --vm b64-padded`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41213) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo [vm] (line 52): `ilo .../ilo/examples/crypto-primitives.ilo --vm hex-abc`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41214) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo [vm] (line 54): `ilo .../ilo/examples/crypto-primitives.ilo --vm ct-eq-yes`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41218) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo [vm] (line 56): `ilo .../ilo/examples/crypto-primitives.ilo --vm ct-eq-no`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41220) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

crypto-primitives.ilo [vm] (line 58): `ilo .../ilo/examples/crypto-primitives.ilo --vm ct-eq-len`
  FAILED (exit exit status: 101)
  stderr: thread 'main' (41222) panicked at src/vm/mod.rs:1877:13:
auto-unwrap on a non-Result tree-bridge builtin slipped past verify
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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