fix(conformance): interop cross-check self-tests require the expected rejection class (LAB-8795)

[27Bslash6]

What

expectRejected in tools/interop-crosscheck.mjs accepted any throw that was not a TypeError or ReferenceError. So a self-test could not tell the rejection it was testing from any other one: an encoder that threw new Error("x") where OutOfModelError belongs still printed OK.

• expectRejected now takes the expected error class and requires err.constructor === errorClass. A different class counts as a failure and is reported as FAIL <test> (<case>): expected <class>, got <class>: <message>. TypeError and ReferenceError are still rethrown as harness bugs.
• The match is exact, not instanceof: OutOfModelError extends Error, so instanceof Error would accept an OutOfModelError in the two self-tests that expect a plain Error.
• All four callers pass their class: loneSurrogateSelftest and unsafeNumberSelftest pass Error; outOfModelSelftest and nonStringKeySelftest pass OutOfModelError.
• The Symbol-key guard's two comment sentences no longer trail the key-sort comment, where "Its data" read as if it meant the byte comparison. They now open their own paragraph above the if, starting "A plain object's data is…". No other comment changes.

No change under spec/, test-vectors/ or tools/interop-reference.py, and no vector bytes change.

Verification

node tools/interop-crosscheck.mjs prints the same line as main: OK: 44 key, 6 value, 6 reader accept, 1 reader reject, 1 AAD, 1 encryption, 34 error vectors verified independently.

Each mutant below was run against this branch and against main's harness:

Mutant	main	this PR
Symbol-key guard throws new Error("x")	exit 0, OK	exit 1, 5 × FAIL nonStringKeySelftest (…): expected OutOfModelError, got Error: x
out-of-model fallthrough throws new Error("x")	exit 1 on 2 reader vectors only	exit 1, same 2 reader vectors plus 7 × FAIL outOfModelSelftest (…): expected OutOfModelError, got Error: x
lone surrogate throws OutOfModelError	exit 0, OK	exit 1, 6 × FAIL loneSurrogateSelftest (…): expected Error, got OutOfModelError: x
unsafe Number throws OutOfModelError	exit 0, OK	exit 1, 6 × FAIL unsafeNumberSelftest (…): expected Error, got OutOfModelError: x
Symbol-key guard removed	exit 1, 5 × expected rejection, encoding succeeded	unchanged
enumerable filter removed	exit 1 on the non-enumerable control	unchanged

python3 tools/conformance.py check OK; python3 tools/test_conformance.py: all 284 cases pass.

Closes LAB-8795

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 4369984 and 1294258.

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📒 Files selected for processing (1)

• tools/interop-crosscheck.mjs

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Summary by CodeRabbit

• Tests
  • Interoperability checks now verify that invalid inputs produce the expected error types and report mismatches. Harness-level type and reference errors remain distinguishable from test failures. This makes test results clearer and easier to interpret. There are no changes to end-user functionality or public interfaces.

Walkthrough

The interop cross-check now validates rejected self-tests against an expected error class. It reports class mismatches and continues to treat TypeError and ReferenceError as harness errors.

Changes

Interop error checks

Layer / File(s)	Summary
Match self-test errors by class tools/interop-crosscheck.mjs	expectRejected now checks the exact error constructor and reports mismatches. The lone-surrogate and unsafe-number tests expect Error; the out-of-model and non-string-key tests expect OutOfModelError. Comments clarify UTF-8 byte ordering and map data.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 12942

The changed error checks match the rejection paths inspected, and no actionable merge-blocking issue remains.

Pre-merge checks | 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check		The title clearly and concisely identifies the main change: self-tests now require the expected rejection class. The issue identifier is relevant.
Description check		The description directly explains the implementation, expected error classes, comment adjustment, verification results, and scope of the change.
Docstring Coverage		Docstring coverage is 83.33% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 1 files.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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