perf(core): reduce noop wait signal overhead

[Ahoo-Wang]

Summary

• Add noop wait-notify benchmark diagnostics for sent waits so the send-and-wait-sent path can be measured independently.
• Optimize waitingLast() for the common single empty-result signal case by returning the original signal instead of copying and merging maps.
• Add a dedicated DefaultCommandGateway.sendAndWaitForSent fast path that bypasses generic wait strategy registration, wait headers, sink subscription, and waitingLast() for the sent convenience API.
• Add regression tests for sent fast-path side effects, error mapping, void command support, single-signal identity, failed prior-stage fallback, and merged wait results.

Changes

• wow-benchmarks: includes WaitNotifyComponentBenchmark in the smoke suite and adds sent wait propagation/notification benchmarks.
• wow-core: extracts wait signal result merging helpers and uses a single-signal fast path in WaitingFor.waitingLast().
• wow-core: updates WaitingForAfterProcessed.waitingLast() to share merge logic while preserving target-stage metadata.
• wow-core: overrides sendAndWaitForSent in DefaultCommandGateway to return a direct SENT result after command bus send succeeds.
• docs/superpowers: records the noop benchmark performance designs used for the implementation.

Benchmark Result

Quick E2E directional result for CommandWriteE2EBenchmark.sendAndWaitSent (scenario=noop-store):

Threads	Before	After	Change
1 throughput	770,645.11 ops/s	1,249,238.49 ops/s	+62.10%
1 allocation	6060.2 B/op	3348.3 B/op	-44.75%
4 throughput	1,190,882.30 ops/s	1,392,839.05 ops/s	+16.96%
4 allocation	6063.1 B/op	3350.2 B/op	-44.74%

Processed noop remained in the same allocation range and is not claimed as optimized by the sent fast path:

Benchmark	Threads	Throughput	Allocation
sendAndWaitProcessed(noop-store)	1	83,973.97 ops/s	6946.8 B/op
sendAndWaitProcessed(noop-store)	4	152,762.87 ops/s	6942.4 B/op

Testing

• ./gradlew :wow-core:test --tests "me.ahoo.wow.command.DefaultCommandGatewayTest"
• ./gradlew :wow-core:test --tests "me.ahoo.wow.command.wait.stage.WaitingForStageNotificationTest" --tests "me.ahoo.wow.command.wait.chain.SimpleWaitingForChainNotifyTest"
• ./gradlew :wow-core:test --tests "me.ahoo.wow.command.wait.*"
• ./gradlew :wow-core:test
• ./gradlew :wow-core:check
• ./gradlew :wow-benchmarks:benchmarkSmoke --stacktrace
• ./gradlew :wow-benchmarks:benchmarkQuickComponentThread1 --stacktrace
• ./gradlew :wow-benchmarks:benchmarkQuickE2E :wow-benchmarks:generateBenchmarkReport --stacktrace

Risk & Compatibility

• No public API signature or dependency changes.
• sendAndWaitForSent(command) no longer writes command_wait_* headers or registers a wait strategy; this is intentional for the sent convenience API because it completes at gateway send success.
• Generic send(command, waitStrategy), sendAndWait(command, waitStrategy), streaming waits, and downstream stage propagation keep the existing wait strategy behavior.
• The waitingLast() single empty-result fast path returns the original emitted WaitSignal, relying on emitted signals not being mutated after emission.

Review Notes

• Review the DefaultCommandGateway.sendAndWaitForSent override as the main behavior change.
• Review WaitingForAfterProcessed.waitingLast() fallback path; it preserves failed previous-stage signals when the target stage never arrives.
• Local benchmark report output was generated for validation but is not included in this PR.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 4 complexity

Metric	Results
Complexity	4

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[codecov]

Codecov Report

❌ Patch coverage is 86.66667% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.65%. Comparing base (c1bdcb8) to head (515aaf1).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...main/kotlin/me/ahoo/wow/command/wait/WaitingFor.kt	71.42%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2690      +/-   ##
============================================
- Coverage     92.67%   92.65%   -0.02%     
- Complexity     4255     4262       +7     
============================================
  Files           753      753              
  Lines         13493    13511      +18     
  Branches        963      966       +3     
============================================
+ Hits          12504    12519      +15     
- Misses          607      609       +2     
- Partials        382      383       +1     

Flag	Coverage Δ
contract	52.53% <80.00%> (?)
integration	76.13% <ø> (?)
local	82.18% <86.66%> (?)

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