fix(runtime): do not export PERRY_AGENT_PTRS on Windows (MSVC TLS export breaks the build)

[proggeramlug]

Summary

Every release build of perry-runtime for x86_64-pc-windows-msvc is broken on main. crates/perry-runtime/src/agent_ptrs.rs declares #[no_mangle] #[thread_local] static PERRY_AGENT_PTRS (added with #11489). MSVC targets cannot export TLS across images, so rustc emits a thread-local shim under the static's own symbol name, and the build fails with "symbol PERRY_AGENT_PTRS is already defined".

The fix is #[cfg_attr(not(windows), no_mangle)]. Only ELF executables name the symbol (perry-codegen/src/expr/agent_ptr.rs); Windows already takes the accessor call. Nothing changes on other targets.

It was found and reproduced with a minimal crate under cargo xwin while rebasing #11565, whose Windows gc-call-effects leg it broke. The same commit is on #11565's branch; landing it separately unblocks Windows builds now.

Validation

• cargo xwin build --release -p perry-runtime --target x86_64-pc-windows-msvc fails before this change and succeeds after it.
• Native cargo check -p perry-runtime is unchanged.

Summary by CodeRabbit

• Bug Fixes
  • Fixed a build issue affecting Windows release versions. Windows builds using MSVC should now complete without the duplicate-symbol error.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: cede5daa-eb73-453d-bc8a-0fc30260f44c

📥 Commits

Reviewing files that changed from the base of the PR and between f702361 and 59e05f2.

📒 Files selected for processing (2)

• changelog.d/11595-windows-agent-ptrs-export.md
• crates/perry-runtime/src/agent_ptrs.rs

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📝 Walkthrough

Walkthrough

The PERRY_AGENT_PTRS declaration now applies no_mangle only on non-Windows targets. Its documentation describes the Windows accessor call, and a changelog entry records the reported MSVC TLS export limitation and duplicate-symbol build failure.

Changes

Agent pointer declaration

Layer / File(s)	Summary
Conditional symbol export crates/perry-runtime/src/agent_ptrs.rs, changelog.d/11595-windows-agent-ptrs-export.md	PERRY_AGENT_PTRS uses cfg_attr(not(windows), no_mangle). The documentation notes that Windows code uses the accessor call. The changelog records the reported MSVC TLS export limitation and duplicate-symbol build failure.

Priority: ➖ Normal

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Bug fix · Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 59e05

The Windows accessor path remains compatible with the conditional TLS export, and non-Windows targets retain the named symbol. No actionable merge-blocking risk is evident.

Architecture Summary

Architecture risk: 🔵 Low · up to 59e05

The change affects 2 systems.

Changed systems: changelog.d, crates

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — changelog.d (service) was modified; 1 changed file maps to changed impact.
• observed — crates (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in changelog.d/11595-windows-agent-ptrs-export.md: Added a changelog entry stating that PERRY_AGENT_PTRS is no longer #[no_mangle] on Windows and describing the reported MSVC TLS export limitation and duplicate-symbol build failure.
• observed — Modified behavior in crates/perry-runtime/src/agent_ptrs.rs: The documentation now describes why the TLS symbol is not exported on Windows and notes that Windows code uses the accessor call. The unconditional no_mangle attribute is replaced with cfg_attr(not(windows), no_mangle), so the attribute applies only on non-Windows targets.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the primary change: preventing Windows/MSVC TLS export issues for PERRY_AGENT_PTRS.
Description check	✅ Passed	The description clearly explains the Windows/MSVC build failure, the code change, its scope, and validation results. It omits several template headings, including Changes, Related issue, and Checklist…

✨ Finishing Touches

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