feat(async): track current running coroutine for graph export

[16bit-ykiko]

Summary

• Add a thread_local async_node* that tracks which coroutine is currently executing on each thread
• Expose async_node::current() and async_node::dump_current_dot() public API so user code inside any coroutine can export the async graph on demand
• Set the thread-local via initial_tracking_suspend (first entry), save/restore in resume() / resume_and_drain() (entry points), and direct assignment in handle_subtask_result() / deliver_deferred() / propagate_fail() (symmetric transfer)

Test plan

• All 643 existing unit tests pass
• CI passes on all platforms

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Added public APIs for introspection of currently executing async nodes: async_node::current() to retrieve the active coroutine node and async_node::dump_current_dot() for state visualization.

• Tests

  • Expanded callable type tests with new tracked callable variants and comprehensive destructor correctness verification across move operations and storage types.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: e76372c0-46af-484e-a337-177819a0e7ad

📥 Commits

Reviewing files that changed from the base of the PR and between 37dc1ed and 0a88804.

📒 Files selected for processing (4)

• include/eventide/async/runtime/frame.h
• include/eventide/async/runtime/task.h
• src/async/runtime/frame.cpp
• tests/unit/common/functional_tests.cpp

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📝 Walkthrough

Walkthrough

This PR introduces thread-local tracking of the currently executing async_node across the coroutine runtime. It adds public APIs (async_node::current(), async_node::dump_current_dot()) and internal detail functions (set_current_node(), current_node()) to track active coroutine nodes. Task coroutine initialization is modified to establish node context, and resume/drain operations now preserve and restore the prior node state through save/restore pairs.

Changes

Cohort / File(s)	Summary
Async Node API Declarations include/eventide/async/runtime/frame.h	Added static methods async_node::current() and async_node::dump_current_dot() to query the active node on the current thread, plus detail-level set_current_node() and current_node() functions for internal tracking management.
Task Coroutine Initialization include/eventide/async/runtime/task.h	Replaced std::suspend_always in task_promise_object::initial_suspend() with initial_tracking_suspend awaitable that establishes the current async_node on first coroutine activation. Updated detail::propagate_fail() to set current node context before returning parent coroutine handle during exception propagation.
Thread-Local Tracking Implementation src/async/runtime/frame.cpp	Implemented thread-local storage (current_running_node) and four new APIs. Enhanced detail::resume_and_drain() and async_node::resume() to save/restore prior node state. Set current node in aggregation delivery paths (aggregate_op::deliver_deferred()) and parent notification paths (async_node::handle_subtask_result()).
Functional Tests tests/unit/common/functional_tests.cpp	Added tracker-based callable structs and comprehensive test cases verifying destructor correctness across SBO/heap storage, move semantics, cross-storage moves, self-assignment, and function_ref/function behavior with various callable types.

Sequence Diagram

sequenceDiagram
    participant Caller
    participant TaskCoro as Task<br/>Coroutine
    participant AsyncNode as async_node
    participant ThreadLocal as Thread-Local<br/>Storage
    
    Caller->>TaskCoro: co_await task
    TaskCoro->>TaskCoro: initial_suspend()
    TaskCoro->>ThreadLocal: set_current_node(this_node)
    ThreadLocal-->>TaskCoro: ✓
    TaskCoro-->>Caller: suspend, return handle
    
    Caller->>AsyncNode: resume()
    AsyncNode->>ThreadLocal: save prior current_node
    ThreadLocal-->>AsyncNode: prior_node
    AsyncNode->>TaskCoro: handle().resume()
    TaskCoro->>TaskCoro: coroutine body executes
    TaskCoro-->>AsyncNode: returns
    AsyncNode->>ThreadLocal: restore prior_node
    ThreadLocal-->>AsyncNode: ✓
    AsyncNode-->>Caller: ✓
    
    Note over TaskCoro,ThreadLocal: Exception path:<br/>propagate_fail() also<br/>sets current_node before<br/>resuming parent

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Possibly related PRs

• feature: add basic async implementation #4: Modifies async_node and thread-local current-node tracking with overlapping APIs and resume behavior changes.
• refactor(async): deduplicate aggregate await_suspend and modernize APIs #49: Updates resume/aggregate control flow paths that directly intersect with the save/restore and current-node bookkeeping added in this PR.
• async: robust async framework #44: Adds similar thread-local "current node" tracking system with dump/current APIs and modify coroutine resume paths.

Suggested reviewers

• fogsong233

Poem

🐰 A thread remembers which node hops along,
Save before resume, restore when done—strong!
No node left behind, context preserved tight,
Coroutines dance in their thread-local light. ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 23.64% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and clearly summarizes the main change: adding thread-local tracking of the current executing coroutine node to enable graph export via public APIs.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/current-node-tracking

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