[backryun]

Part of #8484. Type-only; no toolchain change.

The collisions

BaseExecutor.buildHeaders(credentials, stream?, clientHeaders?, model?, health?) was shadowed in three executors by same-named helpers whose signatures have nothing to do with it:

executor	declared as	signature
hailuo-web	private	(token: string, yy: string)
lmarena	protected	(_model: string, credentials: unknown, _body: unknown)
qwen-web	private	(token: string, cookieHeader: string, chatId?: string)

Name collisions, not overrides — each reported TS2416. Renamed to buildStreamHeaders / buildRequestHeaders / buildApiHeaders, with the two lmarena test files that call the helper directly updated alongside.

Latent, not live — stating it precisely. BaseExecutor.countTokens() calls this.buildHeaders(credentials, false) and all three inherit countTokens(), so the shadow sat on a real dispatch path. It is unreachable today only because buildCountTokensUrl() returns null unless config.format === "claude" and the URL carries /messages; hailuo-web and qwen-web set no format and lmarena sets "openai", so countTokens() returns at the guard one line above. One format change away from passing a credentials object where a token string is expected — but not a bug today, and I'm not going to dress it up as one.

Two more, surfaced by clearing the first

TypeScript reports these one at a time, so each fix revealed the next:

• lmarena narrowed inherited visibility — buildUrl and transformRequest were protected while both are public on BaseExecutor (TS2415: a subclass may widen visibility, never narrow it). Verified identical on the pristine base ref, so pre-existing and masked behind the buildHeaders error. Runtime is unaffected — JavaScript has no member visibility.

• GithubExecutor.refreshCredentials had no declared return type, so TypeScript inferred the union of its four literal returns. GheCopilotExecutor legitimately overrides it with a wider providerSpecificData (it also records the enterprise proxy URL) and no expiresIn — not assignable to that inferred union. Declared as RefreshedCopilotCredentials | null. Same shape of fix as refactor(sse): declare the executor execute() result contract #8489, different method.

Validation

	diagnostics
base	335
this PR	331
new errors	0 (line-number-agnostic diff of the two error sets)

The remaining two TS2416 (felo-web, gitlab — both execute) are #8489's; untouched here.

gate	result
npm run typecheck:core	clean
new tests/unit/ts7-executor-override-signatures.test.ts	10/10
15 existing test files importing a touched executor	pass

Two known base-red conditions, neither caused nor touched here: plan3-p0.test.ts (reads the developer's real ~/.omniroute DB instead of a test-scoped DATA_DIR) and npm run lint (stale suppression count in claude-to-openai-think-close-5123.test.ts). Both are addressed in #8490.

Tests

The renames are behavior-preserving, so the guard targets what actually changed — that the inherited method is no longer shadowed:

assert.equal(executor.buildHeaders, BaseExecutor.prototype.buildHeaders)

Verified to fail on the base, where all three prototypes still carry their own buildHeaders. The suite also pins that each provider keeps its own helper under the new name, and that the countTokens() early return which kept the shadow harmless still holds — so if that guard ever changes, the inherited method is the one that runs.

Overlap note

This touches open-sse/executors/github.ts, as does #8489 — different methods (execute guard there, refreshCredentials signature here) in well-separated regions, so they should auto-merge. Flagging it in case you want a merge order.

[diegosouzapw]

Thanks @backryun — merged into release/v3.8.49 via the local merge-train (validated as one combined tree: full test:unit + test:vitest 274/274 on the 32-core box, tip d4b9ce6016). Your commit keeps its authorship. 🚀