Fix pipe deadlock: drain stdout/stderr concurrently in exec()

[kishikawakatsumi]

Sequential readDataToEndOfFile() calls for stdout then stderr can deadlock when the child process fills the unread pipe's OS buffer while the parent is blocked on the first read.

Changes

• Sources/App/routes.swift: Replace sequential readDataToEndOfFile() with concurrent readabilityHandler callbacks backed by a DispatchGroup. Both pipes are drained in parallel; group.wait() ensures EOF on both before waitUntilExit() is called.

group.enter()
standardOutput.fileHandleForReading.readabilityHandler = { handle in
    let chunk = handle.availableData
    if chunk.isEmpty {
        standardOutput.fileHandleForReading.readabilityHandler = nil
        group.leave()
    } else {
        stdoutData.append(chunk)
    }
}
// same pattern for standardError …

try process.run()
group.wait()
process.waitUntilExit()

[Copilot]

Pull request overview

This PR addresses several correctness and UI-validity issues across the regex debugger, server-side process execution, expression parsing, and the public HTML template.

Changes:

• Fixes a debugger UI event listener leak and corrects backtrack comparisons by using numeric parsing.
• Adjusts server-side Process execution flow to avoid a pipe-related deadlock by changing stdout/stderr read timing.
• Corrects group counting behavior in ExpressionParser and fixes HTML markup errors in index.html.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
Sources/ExpressionParser/ExpressionParser.swift	Stops incrementing groupCount for non-capturing/lookaround group kinds to keep capture numbering correct.
Sources/App/routes.swift	Reorders stdout/stderr reads vs waitUntilExit() in exec(...) to mitigate a process pipe deadlock.
Public/js/app.js	Registers the debugger step-range input handler once during init and fixes backtrack comparison by coercing prior value to Number.
Public/index.html	Fixes invalid HTML by closing <thead> and removing an extra stray closing </span>.

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[Copilot]

Reading stdout and stderr sequentially with readDataToEndOfFile can still deadlock if the child process writes enough data to the other pipe to fill its buffer while the parent is blocked reading the first pipe. To fully address the deadlock, drain stdout and stderr concurrently (e.g., readabilityHandler/DispatchQueue reads into buffers, or redirect both to temporary files) and then wait for termination.

[kishikawakatsumi]

@copilot apply changes based on this feedback

[Copilot]

Fixed in eaff15d. Both stdout and stderr are now drained concurrently using readabilityHandler callbacks that accumulate data into separate buffers. A DispatchGroup tracks when each pipe signals EOF (empty availableData), and group.wait() ensures both streams are fully drained before waitUntilExit() is called — eliminating the buffer-fill deadlock.

[Copilot]

The groupCount semantics changed so that non-capturing/lookaround groups no longer increment the capture numbering. There isn’t currently a test assertion that would catch regressions here (e.g., ensuring the first capturing group after a non-capturing group is still numbered 1). Consider adding an XCTest that parses a pattern like '(?:a)(b)' (and optionally '(?|a(b)|c(d))') and asserts the tooltip substitution/group numbering in the emitted tokens.

[kishikawakatsumi]

@copilot apply changes based on this feedback