feat(blackboard): add GetBlackboardByKey and SetBlackboardByKey for dynamic-key access

[WillYingling]

Summary

Adds a pair of behaviors for reading/writing blackboard entries under runtime-computed keys — the missing primitives for dynamic-key access in BT.CPP v4.

• GetBlackboardByKey — reads an entry whose key is resolved at tick time (typically built via a Script node from other blackboard variables). Mirrors the shape of BT.CPP's native SetBlackboard, which already supports a dynamic output_key port but has no read-side complement. Value copy goes through setOutput<BT::Any> so SubTree auto-remap sentinels ({=}/=) and blackboard-pointer validation are handled by BT.CPP's canonical helper.
• SetBlackboardByKey — write-side complement. Not just a wrapper around SetBlackboard: BT.CPP's native action runs TypeInfo::parseString whenever the source is a string and the destination type is not std::string. Destinations created implicitly by a Script := assignment carry AnyTypeAllowed and have no registered converter, so parseString returns an empty Any and silently clobbers the write. SetBlackboardByKey copies the source Any directly, preserving both type and value.

The @ prefix for root-scope blackboard access is honored transparently in both behaviors (handled inside Blackboard::getEntry / createEntry).

Why

No native dynamic-key read/write pair exists in BT.CPP v4. The conversion bug in SetBlackboard (see above) makes it unsafe for caching script-produced values regardless of whether the key is static or dynamic. These two small primitives fill both gaps.

Motivating use case

Caching pre-computed motion trajectories on the root blackboard during a pre-flight planning pass, then retrieving them during execution in a separate subtree — eliminating duplicated planning calls. Landing in a separate PR against autowash_config.

Test plan

• Registration/instantiation test covers pluginlib loading (test_load_behavior_plugins).
• Functional tick-path tests intentionally deferred — this package currently has no tick-test harness precedent. Validation via the downstream autowash_config regression suite.
• Manual regression confirmed: caching pre-flight trajectories and retrieving them in execution now works end-to-end with SetBlackboardByKey in place (native SetBlackboard produced the empty-Any bug described above).

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds a new BehaviorTree.CPP behavior node to read a blackboard value using a key computed at tick time, enabling dynamic-key cache lookups (including root-scope @ keys).

Changes:

• Introduces GetBlackboardByKey SyncActionNode with key input and value output.
• Registers the new behavior in the plugin loader and library build.
• Extends the existing plugin-load test to instantiate the new node.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/get_blackboard_by_key.cpp	Implements tick-time dynamic-key blackboard read and output propagation.
include/experimental_behaviors/get_blackboard_by_key.hpp	Declares the new behavior and documents its ports/semantics.
src/register_behaviors.cpp	Registers GetBlackboardByKey with the behavior factory.
CMakeLists.txt	Adds the new source file to the shared library build.
test/test_behavior_plugins.cpp	Adds instantiation coverage for the new node in the plugin-load test.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[henrygerardmoore]

LGTM other than one thing; works well where you use it in the autowash config

[henrygerardmoore]

LGTM

[nbbrooks]

To confirm, when this gets merged into core, SetBlackboard should be marked as deprecated?