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URGENT (one-line fix): deliberate offsets must not be gated on guide mode — wrong-object exposure #484

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URGENT (one-line fix): deliberate offsets must not be gated on guide mode — wrong-object exposure #484

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5 changes: 4 additions & 1 deletion acamd/acam_interface.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3644,7 +3644,10 @@ logwrite( function, message.str() );
// and is unaffected.
//
double maxoffset = this->tcs_max_offset;
if ( this->acquire_mode == Acam::TARGET_GUIDE && this->allow_large_offset.load() ) {
if ( this->allow_large_offset.load() ) {

@chatgpt-codex-connector chatgpt-codex-connector Bot Aug 26, 2026

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P1 Badge Keep large-offset permission synchronized with guide state

When offsetgoal races with acquire stop or a new acquisition, allow_large_offset can remain true after acquire_mode leaves TARGET_GUIDE: stopping does not clear the flag, and a new acquisition clears it before changing the mode, allowing another command thread to re-arm it in between. Since acamd processes multiple connections concurrently with the frame-grab loop, removing this predicate lets an in-flight do_acquire() accept up to the 300-arcsec limit and then bypass the guide median filter, sending the correction immediately after a stop or as an acquisition correction rather than enforcing tcs_max_offset. Synchronize the allowance with the associated goal/mode transition instead of honoring the bare flag in every mode.

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@cfremling cfremling Aug 26, 2026 •
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The scenarios described are not failure modes of this change — they are the intended behavior, and none of them are relevant to the defect this fixes.

allow_large_offset is armed by exactly one thing: a deliberate offsetgoal command from the sequencer or an operator. Whatever mode the loop happens to be in when the next correction lands — mid-transition, after a stop, during re-acquisition — executing that deliberate offset is the commanded behavior. "Sending the correction immediately" and "bypassing the guide median filter" for that one correction are both exactly right: a deliberate 72″ science move must not be vetoed by a mode race (measured on sky 2026-08-26: a 6 ms loss exposed 900 s of the wrong object) nor median-filtered against sub-arcsecond guide samples (which would veto it just as silently).

The blast radius of any flag race is already bounded by the existing design: the allowance is one-shot (consumed on use or rejection), ordinary guide corrections remain capped at ACQUIRE_TCS_MAX_OFFSET in every mode because nothing else ever arms the flag, and the absolute 300″ backstop still applies to the consuming correction. The removed predicate provided no protection/it protected against executing exactly what was asked, which is the bug.

If a stricter arm/consume lifecycle (e.g., clearing on acquire stop) is wanted, that is a reasonable, separate hardening change. This PR is the urgent one-line restoration of the correct semantic.

🤖 Generated with Claude Code

// A deliberate goal offset is correct by construction and must not
// be capped as a guide correction, whatever mode the loop is in
// when the correction lands.
maxoffset = this->tcs_max_putonslit_offset;
}

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