cross navigator preemption

[avanmalleghem]

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Basic Info

Info	Please fill out this column
Ticket(s) this addresses	#5886
Primary OS tested on	Ubuntu
Robotic platform tested on	/
Does this PR contain AI generated software?	Claude code was used as a peer reviewer
Was this PR description generated by AI software?	No

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Description of contribution in a few bullet points

• allow_navigator_preemption parameter allows you to start another navigator while another one is running. It will cancel the first one, wait until it is cancelled and then start the new one. Parameter set to false by default so that you keep the current behavior (reject).
• Had to add a flag for internal cancel request (when inside the server you want to cancel the goal). internal_cancel_requested_
• had to swap NavigatorBase and Mutex classes order to create getCurrentNavigator
• In the muxer, current_navigator_ is now a navigator type and not only a string containing its name.

Description of documentation updates required from your changes

• allow_navigator_preemption parameter added

bt_navigator:
  ros__parameters:
    allow_navigator_preemption: true

Description of how this change was tested

• Tested it in simulation (using "navigate_to_pose" and "navigate_through_poses" navigators)

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Future work that may be required in bullet points

For Maintainers:

• Check that any new parameters added are updated in docs.nav2.org
• Check that any significant change is added to the migration guide
• Check that any new features OR changes to existing behaviors are reflected in the tuning guide
• Check that any new functions have Doxygen added
• Check that any new features have test coverage
• Check that any new plugins is added to the plugins page
• If BT Node, Additionally: add to BT's XML index of nodes for groot, BT package's readme table, and BT library lists
• Should this be backported to current distributions? If so, tag with backport-*.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...core/include/nav2_core/behavior_tree_navigator.hpp	48.27%	15 Missing ⚠️

Files with missing lines	Coverage Δ
...ee/include/nav2_behavior_tree/bt_action_server.hpp	83.33% <ø> (ø)
...clude/nav2_behavior_tree/bt_action_server_impl.hpp	89.04% <100.00%> (-1.43%)	⬇️
...core/include/nav2_core/behavior_tree_navigator.hpp	73.97% <48.27%> (-15.32%)	⬇️

... and 5 files with indirect coverage changes

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[SteveMacenski]

@avanmalleghem do you want me to review?

[avanmalleghem]

@SteveMacenski not yet, would like to go deeper in testing before :) I keep you in touch

[avanmalleghem]

parameter.to.true.webm

@SteveMacenski a small video of the expected result :) This PR can be reviewed now... I made a lot of tests in simulation but don't see how I could integrate UT without refactoring code.