Fix Tracker copy semantics: re-point panels and planes at the copy

[oksuzian]

Intent

Panel holds std::array<const Straw*, 96> pointing into the Tracker's own straw array, and Plane holds std::array<const Panel*, 6> pointing into its panel array. Tracker declares no copy constructor, so the compiler-generated one gives the copy fresh straw and panel storage while every Panel and Plane inside it still points at the original object's storage.

The only copy site in Offline today, AlignedTrackerMaker::fromFcl/fromDb (TrackerConditions/src/AlignedTrackerMaker.cc:93,123), is correct only because alignTracker subsequently rebuilds every panel and plane from the copy's own straws. Nothing in TrackerGeom makes that requirement discoverable, so any other copy would silently read another tracker's geometry, and a copy outliving its source would dangle.

Change

• Tracker gets a copy constructor that copies the members and then re-points the constituents at its own content.
• New private helpers Panel::rebindStraws and Plane::rebindPanels do the re-pointing. The two Panel constructors and the Plane constructor now call them instead of repeating the fill loop, so that logic has a single home.
• Tracker is a friend of Panel and Plane for those two helpers; nothing else gains access.

No behavior changes for existing callers: ProditionsEntity deletes assignment, so Tracker stays copy constructible and non-assignable, and the only std::move involving a tracker (TrackerMaker::getTrackerPtr) moves a unique_ptr, not a Tracker.

Deliberately not changed: the TrackerG4Info shared_ptr is still shared with the original rather than deep copied. It describes the nominal G4 model and does not depend on the (possibly aligned) straw positions.

Validation

Compiled the changed translation units, plus the three main consumers, with the Muse spack toolchain (gcc 13.3, -std=c++20 -Wall -Werror): all of TrackerGeom/src/*.cc, TrackerConditions/src/AlignedTrackerMaker.cc, GeometryService/src/TrackerMaker.cc and Mu2eG4/src/ConstructTrackerDetail5.cc pass.

Wrote a throwaway program that builds a Tracker from a synthetic straw set, copies it, and counts constituent pointers that do not fall inside the copy's own arrays. Against main:

straw pointers not owned by the copy: 20736 / 20736
panel pointers not owned by the copy: 216 / 216

With this branch:

straw pointers not owned by the copy: 0 / 20736
panel pointers not owned by the copy: 0 / 216

The program is not included here; TrackerGeom has no test directory and I did not want to add one in this PR. Happy to contribute it wherever the collaboration would want such a check to live.

I have not run a full build or the physics validation jobs locally; leaving that to CI.

Related, not addressed here

While reading the package I noticed a few adjacent items that are separate topics and are deliberately left out to keep this PR to one thing: the Panel/Plane pointer arrays are not value initialised in the value constructors and no check catches an unfilled slot; Panel.cc hardcodes straws 47/48 as the panel middle while Plane.cc divides by a literal 6; Tracker::_origin is never assigned; and Manifold/ManifoldId appear to be dead but are still built. I can open follow-ups if they are wanted.

🤖 Generated with Claude Code

https://claude.ai/code/session_0138sWPyeSCDFbbn2cB9JBDy

[FNALbuild]

Hi @oksuzian,
You have proposed changes to files in these packages:

• TrackerGeom

which require these tests: build.

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⌛ The following tests have been triggered for c350c73: build (Build queue - API unavailable)

About FNALbuild. Code review on Mu2e/Offline.

[FNALbuild]

☀️ The build tests passed at c350c73.

Test	Result	Details
test with	✅	Command did not list any other PRs to include
merge	✅	Merged c350c73 at c4b2bc6
build (prof)	✅	Log file. Build time: 04 min 22 sec
ceSimReco	✅	Log file.
g4test_03MT	✅	Log file.
transportOnly	✅	Log file.
POT	✅	Log file.
g4study	✅	Log file.
cosmicSimReco	✅	Log file.
cosmicOffSpill	✅	Log file.
ceSteps	✅	Log file.
ceDigi	✅	Log file.
muDauSteps	✅	Log file.
ceMix	✅	Log file.
rootOverlaps	✅	Log file.
g4surfaceCheck	✅	Log file.
trigger	❓	Log file. Return Code 1.
check_cmake	✅	Log file.
FIXME, TODO	➡️	TODO (2) FIXME (4) in 6 files
clang-tidy	➡️	2 errors 17 warnings
whitespace check	✅	no whitespace errors found

N.B. These results were obtained from a build of this Pull Request at c350c73 after being merged into the base branch at c4b2bc6.

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