docs: fix doc drift in pending_signature_queue_len

[netrome]

closes #3270

[Copilot]

Pull request overview

This PR fixes documentation drift for the sandbox-only pending_signature_queue_len view method, clarifying that it only consults the fan-out map and is authoritative for fresh sandbox state.

Changes:

• Updates the method comment to remove the outdated claim that post-upgrade pushes drain legacy entries into the new queue.
• Clarifies the legacy map is intentionally not consulted by this sandbox helper.

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[claude]

Pull request overview

This PR fixes doc drift in the pending_signature_queue_len sandbox helper. The previous comment claimed that "post-upgrade pushes drain [the legacy single-yield map] into the head of the new queue," which is not what the code actually does — push_pending_yield always writes to the new fan-out map and leaves the legacy map untouched (crates/contract/src/pending_requests.rs:96). The corrected wording scopes the "authoritative length" claim to sandbox tests that start from fresh state, where no legacy entries can exist.

Changes:

• Reword the doc comment on pending_signature_queue_len to remove the incorrect "drain into the head of the new queue" claim and replace it with the accurate fresh-state qualifier.

Reviewed changes

Per-file summary

File	Description
crates/contract/src/sandbox_test_methods.rs	Doc-only change on pending_signature_queue_len; behavior unchanged.

Findings

No blocking or non-blocking issues. The new wording is consistent with push_pending_yield / resolve_yields_for / pop_one_yield_for in crates/contract/src/pending_requests.rs, and pending_ckd_queue_len directly below already refers back to this comment via "same rationale," so the single-location fix is sufficient.

✅ Approved