Enforce plain node:assert test style: migrate node:assert/strict usages + add oxlint no-restricted-imports #1555

Problem

AGENTS.md (test-style section, ~line 195) makes plain node:assert the house style for new tests and explicitly rules out node:assert/strict ("strict mode's deep-equality and coercion rules cause more friction and surprising failures than they prevent"). But the convention isn't enforced and the codebase overwhelmingly violates it:

• 208 test files import node:assert/strict vs 29 on plain node:assert (unitTests + integrationTests).
• Even the "target-shape" dirs AGENTS.md names are mostly /strict: unitTests/config 11, unitTests/resources 25, unitTests/components 48.

The only thing catching new /strict usage today is the AI reviewer, which raises it as a non-blocking suggestion on every affected PR — recurring noise that never gets systematically resolved (see e.g. PR #1106).

Goal

Make the documented convention deterministic — caught by CI's linter before review — so the reviewer nit disappears and new code can't regress.

The rule to standardize on: default to require('node:assert'); never import node:assert/strict; when a specific assertion genuinely needs strict/deep-strict semantics, call assert.strictEqual / assert.deepStrictEqual explicitly (both available from plain node:assert). This keeps strictness opt-in and visible at the call site rather than silently applied to every assert.equal by the import.

Plan

1. Migrate existing node:assert/strict imports → node:assert across test files. This is mechanical and safe: strict→loose only ever weakens an assertion, so no currently-green test can turn red. (Optionally, spot-convert assertions that should stay strict to explicit strictEqual/deepStrictEqual.) Consider staging by dir — the target-shape dirs (config/resources/components, ~84 files) first.
2. Enforce with oxlint no-restricted-imports so regressions fail runLinter:

   "no-restricted-imports": ["error", { "paths": [
     { "name": "node:assert/strict", "message": "Use plain node:assert; call assert.strictEqual/deepStrictEqual for strict checks (AGENTS.md house style)." },
     { "name": "assert/strict" }
   ]}]

   Can be scoped to unitTests/{config,resources,components}/** first via oxlint overrides, then widened as legacy dirs are migrated.

Notes

• oxlint supports no-restricted-imports (verified against the installed version's rule list).
• Enabling the rule repo-wide before migrating will fail lint on the 208 existing files — hence migrate first (or scope via overrides).
• Older unitTests/security/* and unitTests/utility/* are not the target shape (they also use sinon/rewire per AGENTS.md); their imports are still safe to migrate but can be de-prioritized.
• Pattern to follow: PR feat(models): add openaiStream() OpenAI-compatible SSE formatter #1106 already switched the two openaiStream test files to plain node:assert — use as the reference for the mechanical change.

Acceptance

• No node:assert/strict imports remain in the enforced scope.
• oxlint no-restricted-imports rule added and green in CI.
• AGENTS.md test-style note updated to point at the lint rule as the enforcement mechanism.

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