chore(deps): bump z3 from 0.20.2 to 0.21.0

[dependabot]

Bumps z3 from 0.20.2 to 0.21.0.

Commits

• 1514267 chore: release (#574)
• bbd49f4 chore: Update README.md
• 82c5448 chore: bump z3-sys to use 5.1.0 by default (#585)
• 66f09e9 chore: release z3-src (Z3 z3-5.1.0) (#584)
• 3606767 feat!: auto-detect z3 version (#583)
• 40d92eb feat: Optimize::set_model_handler (#577)
• 385eb26 Don't build xtask tool in wasm cross-compile (#580)
• 70081be fix: add missing inc_ref to ApplyResult's Clone (#578)
• e717cdd chore: bump z3 to use z3-sys 0.12.0 (#575)
• 60eae85 chore(z3-sys): release v0.12.0 (#571)
• Additional commits viewable in compare view

[github-actions]

🔒 HELD — not auto-mergeable (class: zerox-minor). 0.20.2 -> 0.21.0: for a 0.x crate the MINOR is the de-facto major (ordeal 0.9->0.12; object 0.39->0.40 / #938)

Auto-merge has been actively disabled and asserted off by the hold gate (#965). For a 0.x crate the MINOR component is the de-facto major (and for 0.0.x, the patch): ordeal 0.9→0.12 auto-merged as "minor" and hung Test+Z3 for days; object 0.39→0.40 (#938) broke 16 call sites across three unrelated newtype surfaces. Merge this BY HAND only once the FULL suite is green, including the separate --features z3-solver path (required context "Z3 Verification") — the discriminator is CI, not a read of the diff.

[github-actions]

🔒 HELD — not auto-mergeable (class: zerox-minor). 0.20.2 -> 0.21.0: for a 0.x crate the MINOR is the de-facto major (ordeal 0.9->0.12; object 0.39->0.40 / #938)

Auto-merge has been actively disabled and asserted off by the hold gate (#965). For a 0.x crate the MINOR component is the de-facto major (and for 0.0.x, the patch): ordeal 0.9→0.12 auto-merged as "minor" and hung Test+Z3 for days; object 0.39→0.40 (#938) broke 16 call sites across three unrelated newtype surfaces. Merge this BY HAND only once the FULL suite is green, including the separate --features z3-solver path (required context "Z3 Verification") — the discriminator is CI, not a read of the diff.

[avrabe]

[maintainer loop] Held-state audit — recording measured status so this hold is not silent.

z3 0.20.2 -> 0.21.0 · classifier: class=zerox-minor

All 9 required contexts are GREEN on this PR. The only red is
Rivet Federated Graph (advisory), which was failing repo-wide from
2026-09-03 04:00–21:25 because GitHub rate-limits anonymous clones from
datacenter IPs — nothing to do with this bump. Diagnosed and fixed in #1143/#1144.

So this is held by policy, not by evidence of breakage. The policy
(SYNTH-DEPENDABOT-MINORHOLD-ENFORCED-965) treats a 0.x minor as a de-facto
major, because for a 0.x crate it is one — earned from ordeal 0.9 -> 0.12,
which auto-merged as "minor" and hung Test/Z3 for 4–6 hours per run for
days.

Why you are being told this rather than left to rot. A held PR currently has
no defined exit: it cannot auto-merge, and nothing prompts a human. Four of
these accumulated since 2026-08-31 — one (#1111, wasmparser) was genuinely
source-breaking and is closed with that evidence; the rest were reporting a CI
outage, not an incompatibility. A hold that is correct and silent is how they
became invisible, and I described their state wrongly in the org review as a
result. Raised for temper in #1132.

Staying held pending a deliberate decision, not forgotten. If you want it taken,
say so on this PR.

[github-actions]

🔒 HELD — not auto-mergeable (class: zerox-minor). 0.20.2 -> 0.21.0: for a 0.x crate the MINOR is the de-facto major (ordeal 0.9->0.12; object 0.39->0.40 / #938)

Auto-merge has been actively disabled and asserted off by the hold gate (#965). For a 0.x crate the MINOR component is the de-facto major (and for 0.0.x, the patch): ordeal 0.9→0.12 auto-merged as "minor" and hung Test+Z3 for days; object 0.39→0.40 (#938) broke 16 call sites across three unrelated newtype surfaces. Merge this BY HAND only once the FULL suite is green, including the separate --features z3-solver path (required context "Z3 Verification") — the discriminator is CI, not a read of the diff.