fix: Preserve error chains across error wrapping boundaries

[dcramer]

Six locations wrapped errors without passing { cause: error }, breaking error chain traversal for debugging and Sentry reporting. Also adds a code property to ExecError for structured errno access.

Changes

• src/cli/git.ts: Add { cause: error } to git() wrapper
• src/sdk/errors.ts: Update WardenAuthenticationError to accept { cause } option
• src/sdk/auth.ts: Pass cause to WardenAuthenticationError throws
• src/sdk/analyze.ts: Pass cause when rethrowing auth errors
• src/skills/remote.ts: Pass cause to SkillLoaderError in execGit
• src/evals/index.ts: Pass cause to file read error wrapper
• src/utils/exec.ts: Add code property to ExecError, populate from spawn errors

Automated fix for Warden findings bf3caddd, 811a555f, 410d3c52, 91113dcf, ebd7c6df, cd7521bb (medium, detected by find-warden-bugs).

Ref #212

This PR was auto-generated by a Warden Sweep (run cd745cc3).
The finding has been validated through automated deep tracing,
but human confirmation is requested as this is batch work.

[sentry-warden]

ExecError wrapping discards original error chain

The PR claims to fix error chain preservation, but lines 73 and 107 still wrap result.error without passing { cause: result.error }. Additionally, the ExecError constructor (line 6-18) doesn't accept an options parameter to support { cause } - the super() call only passes the message string, not options. This breaks error chain traversal for debugging and Sentry reporting when spawn errors occur.

Verification

Read src/utils/exec.ts and verified: (1) The ExecError constructor at lines 6-18 has signature constructor(command, exitCode, stderr, signal, code?) with no options parameter for cause. (2) The super() call at line 15 passes only the message, not { cause }. (3) Lines 73 and 107 pass result.error.message and the code but not the error itself as cause.

Suggested fix: Update ExecError constructor to accept an options parameter with cause, and pass the original error when throwing

Suggested change

	throw new ExecError(command, null, result.error.message, null, (result.error as NodeJS.ErrnoException).code);
	public readonly code?: string,
	options?: { cause?: unknown }
	super(`Command failed: ${command}\n${details}`, options);

Identified by Warden find-warden-bugs · QV3-B7G