DelayLine.Process with an out-of-range delay throws after writing the sample, so a rejected call still shifts every later tap by one sample

[matt-edmondson]

What's wrong

DelayLine.Process(float input, int delaySamples) (Containers/DelayLine.cs ~line 152) is implemented as:

Write(input);
return Read(delaySamples);

The range check on delaySamples (ThrowIfNegative / ThrowIfGreaterThan(delaySamples, Capacity)) lives in Read, so it only runs after Write has stored the sample and advanced the write cursor.

Repro (verified by running against the current main)

var line = new DelayLine(4);
try { line.Process(99f, 5); } catch (ArgumentOutOfRangeException) { }
Console.WriteLine(line.Read(0)); // expected 0 (the call was rejected), actual 99

Why it matters

The call throws, so the caller treats it as rejected, but the delay line's state has still changed. The write cursor has moved and a sample the caller thinks was discarded is now in the buffer. Every later read is off by one sample relative to the caller's own sample count. In an audio callback that catches and carries on, this puts a click into the output and shifts the timing of every tap.

Suggested fix

Validate before mutating. Either:

• add ArgumentOutOfRangeException.ThrowIfNegative(delaySamples); ArgumentOutOfRangeException.ThrowIfGreaterThan(delaySamples, Capacity); at the top of Process, or
• move the check into a small shared helper that both Read and Process call before doing anything.

Acceptance criteria

• Process with a negative delay, or a delay above Capacity, throws ArgumentOutOfRangeException and leaves the buffer contents and write position unchanged.
• A test that covers the repro above.

[matt-edmondson]

Triage

• Category: Bug (a rejected call still changes state)
• Priority: Medium. It only fires on an argument the caller got wrong, but a call that throws and still changes the buffer breaks the usual contract. In a catch-and-continue audio callback it causes an audible click and a permanent one-sample timing shift.
• Area / suggested assignment: Containers/DelayLine.cs (Process, Read). Validate before Write, with a shared guard helper.
• Duplicates: none. It is in the same class as DelayLine.ReadInterpolated(Capacity) returns the newest sample instead of the oldest when Capacity is 2^k − 1 (k ≥ 25), and Capacity + 1 doesn't throw #93 (ReadInterpolated bounds) and RingBuffer, SpscRingBuffer and DelayLine throw an undocumented OverflowException for sizes above 2^30, and a failed RingBuffer.Resize corrupts the buffer #89 (sizing overflow). Anyone working on DelayLine bounds should take all three together.
• In progress: no. There are no open PRs in this repo.

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