harness: match explicit trap equivalences exactly

[lannbot]

Summary

• Match explicit trap-diagnostic equivalences by full expected and actual message equality. Keep ordinary WAST actual.includes(expected) matching unchanged.
• Enumerate the previously verified handle-index messages instead of broad expected prefixes; use full engine guest trapped: messages, including the observed Bun/JSC evaluating suffix as an exact string.
• Add positive exact-pair and negative affix/poison-cause tests. No regex, prefix, suffix, stripping, or normalization fallback in explicit equivalences.

The seven recently added mapping categories need no extra rows. Converting older handle prefix entries adds six exact rows. Runtime and corpus expectations are unchanged.

Verification

• Independent review: LGTM; final runner unit suite17passed.
• Full just gates < /dev/null sequence completed across the initial run and interrupted-browser continuation: /tmp/opencode/exact-diagnostic-gates.log, /tmp/opencode/exact-diagnostic-remaining-gates.log.
• Official conformance unchanged:1286 passed commands,125xfail,95pending-runtime,5unsupported-directive,0unexpected failures.
• Supplementary Wasmtime unchanged:570passes,102classified failures,4skips,174excluded commands,0unexpected/infra failures.
• Required SpiderMonkey/Node and Chromium/Firefox page/worker/shared-worker and allOPFS gates passed. JSC shell unavailable onarm64 as configured.
• Initial findings-only Bun lane exposed its full RuntimeError suffix; after explicitly enumerating that observed spelling, runner tests and just shell-lane bun-pinned passed with1286pass/125xfail/0failed. No wildcard or expectation added.
• Packaging and available consumer smokes passed; consumer statuses unchanged. Existing deferred/profile/optional-fixture exclusions and translation-only consumer legs remain.

No runtime code, manifests, protocol, goldens, or failure expectations changed. Automerge will be armed and watched through delivery.