fix(sse): retry advisor 400 with unreadable results marked unavailable

[cryptiklemur]

Summary

• Anthropic encrypts each advisor_redacted_result for the org that made it. when a Claude conversation moves to another account, the new account cant read those results. the request fails with a 400: "Advisor tool result content could not be processed."
• on that exact 400, BaseExecutor now retries once on the same connection. each advisor_tool_result holding an advisor_redacted_result gets its content swapped for { type: "advisor_tool_result_error", error_code: "unavailable" }. the paired server_tool_use and every other block stay as they are.
• if the retry fails too, the response falls through to the normal fallback chain.
• the swap sticks for later fallback URLs in the same execute() call, so they dont re-hit the same 400.
• helpers live in open-sse/config/providerFieldStrips.ts: isAdvisorUndecryptableError() and replaceRedactedAdvisorResults().
• also removes four imports in open-sse/executors/base.ts that are unused on this branch, and voids the unused health param. that clears the 5 no-unused-vars suppressions for the file, so its entry is pruned from config/quality/eslint-suppressions.json.

Related Issues

• none filed.

Validation

• Change type: provider
• Focused tests and category gates from the golden path
• npm run lint: no errors. it exits 2 only because release/v3.8.51 has 5 stale suppressions in unrelated files (openai-to-cursor.ts, SystemStorageTab.tsx, both vscode combos/route.ts, ghe-copilot.ts). the same happens on the base, and --pass-on-unpruned-suppressions exits 0.
• Reconciled with the current active release base; focused checks rerun afterward
• Production-code changes include a new or updated automated test in this PR

check	result
new test with helpers only, no base.ts change	2 of 6 fail (no retry happens)
new test with the fix	6 of 6 pass
base-executor-*, executor-base-utils, field-400-downgrade, param-filters-auto-learn, provider-field-strips, reasoning-effort-clamp-and-retry, context-editing-executor-injection	150 of 150 pass
eslint (with suppressions) + prettier on touched files	clean
live	tested on a real cross-account Claude conversation; the retry returned 200

Tests Added Or Updated

• tests/unit/base-advisor-undecryptable-retry.test.ts (new)

Coverage Notes

• the test covers the retry and its body, a second failure (no second retry), an unrelated 400, the advisor 400 with no redacted result in the body, the exact-message match, and the no-op case.

Reviewer Notes

• the match is on the exact error.message string. a reworded Anthropic message will skip the retry and fail the way it does today.
• the model loses the old advisor advice for that turn. it sees an unavailable advisor error instead of a hard failure.

[diegosouzapw]

Thanks @cryptiklemur — merged into release/v3.8.52; it ships in the next release.