Add post-append side-effect parity to the DCB application service

[johanhaleby]

What

Gives the DCB application service post-append side-effect parity with the stream application service. GenericApplicationService runs a side-effect on the newly written events after a successful write, so a command can trigger a policy. The DCB application service had no equivalent, so a DCB command could not.

This is PR5 in the DCB stack.

How

• DcbExecuteOptions<E> carries an optional post-append side-effect, with options() / empty() factories and a sideEffect(...) builder.
• DcbApplicationService gains execute(query, options, fn) as the primary overload. The existing execute(query, fn) now delegates to it with empty options, so callers are unaffected.
• GenericDcbApplicationService mirrors the stream timing exactly: read, domain function, convert, tag, and append run inside the retry, and the side-effect runs once after the retry succeeds, with the newly written domain events. It does not run on the no-new-events path and not per retry attempt.
• The store-agnostic PolicySideEffect is reused as-is, not duplicated. Kotlin gets a reified dcbSideEffect builder (single policy and two-policy compose).

The one intentional divergence from the stream options

DcbExecuteOptions has no read-filter option, unlike the stream ExecuteOptions. In DCB the DcbQuery passed to execute is both the read filter and the consistency boundary, so a separate filter here would be redundant and misleading. The Javadoc states this so the asymmetry is not mistaken for an oversight.

Decider extensions

Left as-is. A decider caller that wants a side-effect uses execute(query, options, fn) with a decider-built function, which avoids multiplying the decider overload surface (decision, state, events, single and list command) for marginal value. Flagging this as a deliberate scope call.

Tests

• DcbApplicationServiceSideEffectTest: the side-effect runs once with the written events, does not run when the domain function produces no events, a reused PolicySideEffect discriminates by event type, and the simple execute(query, fn) still appends.
• DcbExecuteOptionsExtensionsTest: the Kotlin reified dcbSideEffect builder fires for the matching type and composes two policies.
• The stream GenericApplicationServiceTest side-effect and retry tests pass unchanged (backward compat).

[github-actions]

Qodana Community for JVM

74 new problems were found

Inspection name	Severity	Problems
Kotlin Maven Plugin misconfigured	🔶 Warning	27
Constant values	🔶 Warning	25
Nullability and data flow problems	🔶 Warning	14
'Optional' used as field or parameter type	🔶 Warning	2
Pointless boolean expression	🔶 Warning	2
'equals()' called on classes which don't override it	🔶 Warning	1
Result of method call ignored	🔶 Warning	1
Function or property has platform type	◽️ Notice	2

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[Copilot]

Pull request overview

Adds post-append side-effect support to the blocking DCB application service so DCB commands can trigger policies after a successful append, matching the stream-based application service’s side-effect timing semantics.

Changes:

• Introduces DcbExecuteOptions<E> carrying an optional post-append side-effect, plus Kotlin convenience builders (dcbExecuteOptions, dcbSideEffect).
• Extends DcbApplicationService/GenericDcbApplicationService with an execute(query, options, fn) overload and runs the side-effect once after a successful append (not on no-new-events, not per retry).
• Adds Java/Kotlin tests validating side-effect behavior and typed policy composition.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
changelog.md	Documents the new DCB post-append side-effect option and its intended semantics.
application/service/blocking/src/main/java/org/occurrent/application/service/blocking/dcb/DcbApplicationService.java	Adds the options-based execute overload and delegates from the simpler overload.
application/service/blocking/src/main/java/org/occurrent/application/service/blocking/dcb/GenericDcbApplicationService.java	Implements side-effect execution once after successful retry+append, returning Optional.empty() on no-new-events.
application/service/blocking/src/main/java/org/occurrent/application/service/blocking/dcb/DcbExecuteOptions.java	New options type holding an optional post-append side-effect (no read-filter by design).
application/service/blocking/src/main/kotlin/org/occurrent/application/service/blocking/dcb/DcbExecuteOptionsExtensions.kt	Kotlin helpers for creating options and typed PolicySideEffect side-effects.
application/service/blocking/src/test/java/org/occurrent/application/service/blocking/dcb/DcbApplicationServiceSideEffectTest.java	Verifies side-effect runs once with newly appended events and not on no-new-events.
application/service/blocking/src/test/kotlin/org/occurrent/application/service/blocking/dcb/DcbExecuteOptionsExtensionsTest.kt	Tests Kotlin dcbSideEffect typed filtering and composition.

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[Copilot]

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

[johanhaleby]

Landed via the consolidated #234.