[codex] Structure process diagnostics failures

[juliusmarminge]

Summary\n- attach bounded command metadata, working directory, timeout, exit status, and output byte/truncation counts to diagnostics failures\n- preserve exact spawn causes without deriving messages from them or retaining raw process streams\n- include both target and server PIDs when rejecting non-descendant processes

Tests

• vp test apps/server/src/diagnostics/ProcessDiagnostics.test.ts
• vp check
• vp run typecheck

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Note

Low Risk
Changes are confined to diagnostics error shaping and messages; behavior of successful reads/signals is unchanged, though alert rules matching old error strings may need updates.

Overview
Process diagnostics failures now carry structured fields instead of relying on stderr text for messages.

Query errors (ProcessDiagnosticsQueryTimeoutError, ProcessDiagnosticsQueryFailedError) gain argCount, cwd, and (for timeouts) timeoutMillis; failed queries also record exitCode plus bounded stdout/stderr byte counts and truncation flags. User-facing messages mention cwd, timeout, and exit code—not raw stderr.

runProcess captures cwd and stream collection metadata once and threads it into both POSIX (ps) and Windows (powershell.exe) failure paths. ProcessDiagnosticsNotDescendantError now includes serverPid alongside the target pid.

A new test asserts failed ps exits produce the expected structured error and message format.

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Note

Structure process diagnostics errors with bounded command metadata

• ProcessDiagnosticsQueryFailedError is extended with argCount, cwd, exitCode, stdoutBytes, stderrBytes, stdoutTruncated, and stderrTruncated fields; the raw stderr string is removed from the error.
• ProcessDiagnosticsQueryTimeoutError gains argCount, cwd, and timeoutMillis fields with an updated message format.
• ProcessDiagnosticsNotDescendantError gains a serverPid field.
• The ProcessOutput interface and runProcess function in ProcessDiagnostics.ts now capture cwd and output byte counts/truncation flags on every execution.
• Behavioral Change: error message formats for timeout and failure errors have changed; callers inspecting the stderr field of ProcessDiagnosticsQueryFailedError will need to use stderrBytes instead.

^{Macroscope summarized 44734fa.}

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[macroscopeapp]

Approvability

Verdict: Approved

This PR adds structured diagnostic fields to error classes for better error reporting. The changes are additive, don't alter control flow, include tests, and are authored by the file's primary maintainer.

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Dismissing prior approval to re-evaluate 44734fa