fix(diag): remove dead string-wrapper counter

[proggeramlug]

Boxed string indices became virtual in #9810, which removed the only writer for the STRING_WRAPPERS diagnostic while leaving its state and output branch in place. The impossible counter and its stale GC-holder inventory exemption are now removed; the live primitive-method histogram and receiver-length attribution remain unchanged.

Validation:

• Repository-wide scan confirms there is no remaining STRING_WRAPPERS, writer alias, or string_wrappers= output site
• gc_runtime_root_holders.py self-test and inventory check pass: 1,357 declarations scanned, 347 valid inventory entries
• scripts/run_lint_gates.sh: all 64 gates passed, 2 CI-only checks skipped locally
• No version bump

Fixes #9874

Summary by CodeRabbit

• Bug Fixes
  • Updated garbage-collection diagnostics to remove outdated string-wrapper counts.
  • Primitive dispatch reports now show only active method-call and receiver-character statistics.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Team

Run ID: 9e2cd2e9-728e-42fb-a18c-d1441b5ae55f

📥 Commits

Reviewing files that changed from the base of the PR and between 0866940 and e991e1c.

📒 Files selected for processing (3)

• changelog.d/9900-dead-string-wrapper-diag.md
• crates/perry-runtime/src/gc/diag_sites.rs
• scripts/gc_runtime_root_holders.json

💤 Files with no reviewable changes (1)

• scripts/gc_runtime_root_holders.json

Included review availability: Your plan provides up to 8 included reviews per hour; 5 remain after this review.

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📝 Walkthrough

Walkthrough

The change removes the unwritable STRING_WRAPPERS counter from GC primitive-dispatch diagnostics, deletes its root-holder entry, updates the related comment, and adds a changelog entry.

Changes

GC diagnostic cleanup

Layer / File(s)	Summary
Remove dead counter crates/perry-runtime/src/gc/diag_sites.rs, scripts/gc_runtime_root_holders.json, changelog.d/9900-dead-string-wrapper-diag.md	The STRING_WRAPPERS counter and its holder entry were removed. The primitive-method fallback comment was updated. The changelog records the diagnostic fix.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to e991e

GC primitive-dispatch diagnostics no longer emit the obsolete zero-valued string-wrapper counter; the remaining diagnostic histogram and process-exit reporting behavior remain intact. No current merge-readiness risk is identified.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: removing the dead string-wrapper diagnostic counter.
Description check	✅ Passed	The description explains the cause, the implemented removal, the affected diagnostics, linked issue, validation results, and version-bump status. It does not use every template heading or checklist it…
Linked Issues check	✅ Passed	The PR satisfies issue #9874 by removing the unwritable STRING_WRAPPERS counter, its unreachable output branch, and its stale GC-holder inventory entry. The live diagnostic logic remains unchanged.
Out of Scope Changes check	✅ Passed	All changes support the linked issue: the diagnostic counter, its output, the related inventory entry, and the changelog documentation. No unrelated code changes are present.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 1 files. (1 skipped: 1 …

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[proggeramlug]

Landed on main via merge train #9903. Validated as a tree: 64/64 lint gates, and perry-runtime/codegen/hir/stdlib all green (5,944 tests, 0 failures). Thanks!