Migrate the reaction events and response to the generated ReactionResponse

[gpunto]

Goal

Parse the three reaction events and the reaction response with the generated ReactionResponse, retiring
DownstreamReactionDto.

Part of AND-1291

Implementation

• Point reaction on reaction.new, reaction.updated and reaction.deleted, and on the hand-written
  ReactionResponse wrapper, at the generated model. It was already vendored and already mapped, since
  latest_reactions and own_reactions migrated earlier, so this adds no mapper.
• Delete DownstreamReactionDto with its adapter, its registration and its mapper, and drop its
  reflection warm-up, which already covers the generated model. ReactionDtoAdapters.kt becomes
  UpstreamReactionDtoAdapter.kt, since the upstream adapter is all it still holds.
• Require created_at, updated_at and user in the direct ReactionAdapter too, so both parsing paths
  reject the same payloads.
• Rebuild the reaction parser fixtures around the real wire shape. They previously omitted user,
  created_at and updated_at, none of which is optional: every field on payload.ReactionResponse is a
  plain non-omitempty tag and its user is the full commonpayloads.UserResponse. The four
  jsonMissing* fixtures omitted them too, so once the model tightened those tests would have thrown for
  the wrong reason and still passed. Only custom data is optional now.

Notes

Three fields go from optional to required: created_at, updated_at and user. All three are plain tags
on the payload struct, and the seven fields UserResponse requires are plain tags on
UserResponseCommonFields, so the backend sends them whatever the hydration.

reaction.deleted was the one to check, since poll.deleted ships a lean payload. It does not: all three
events embed the same *payload.ReactionResponse.

emoji_code is custom data rather than a declared field, so it arrives in custom. The existing mapper
already promotes it and keeps it out of extraData.

The E2E mock server synthesises reactions in src/helpers/reactions.rb. Checked: it starts from the
recorded payload and overwrites the user with one that carries all seven required fields.

Testing

No mutation sweep: this slice adds no mapper, so a sweep would mutate code it does not touch.

Device-probed the send response, the update, delete, a channel query, and all three events. Every field of
each Reaction asserted rather than only the changed ones, including a sentinel in extraData that
round-tripped on both the response and the event path, which is what proves custom data is collected and
read back rather than silently dropped. The nested user came back with language empty, the zero value the
wire sends when it is unset, which the required non-null field accepts.

Summary by CodeRabbit

• Bug Fixes
  • Improved reaction event parsing and mapping for more consistent handling across chat events.
  • Reaction payloads now require creation time, update time, and user information, helping detect incomplete data instead of accepting malformed reactions.
  • Preserved custom reaction fields, including fields with names that overlap with built-in model functions.
  • Updated reaction handling to consistently use the standard reaction response format.

[github-actions]

PR checklist ✅

All required conditions are satisfied:

• Title length is OK (or ignored by label).
• At least one pr: label exists.
• Sections ### Goal, ### Implementation, and ### Testing are filled, or the PR is bot-authored.
• An issue is linked (Linear ticket or GitHub issue), or the PR is bot-authored.

🎉 Great job! This PR is ready for review.

[github-actions]

SDK Size Comparison 📏

SDK	Before	After	Difference	Status
stream-chat-android-client	6.08 MB	6.07 MB	-0.00 MB	🚀
stream-chat-android-ui-components	11.39 MB	11.39 MB	-0.00 MB	🚀
stream-chat-android-compose	13.06 MB	13.05 MB	-0.00 MB	🚀

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Walkthrough

The pull request removes DownstreamReactionDto, changes reaction event and response models to use ReactionResponse, updates parser behavior, and revises reaction fixtures and tests.

Changes

Reaction model consolidation

Layer / File(s)	Summary
Reaction contract and wiring stream-chat-android-client/src/main/java/io/getstream/chat/android/client/..., stream-chat-android-client/src/main/java/io/getstream/chat/android/client/api2/...	Removes DownstreamReactionDto and its domain mapping. Event and response models now use ReactionResponse.
Reaction parser behavior stream-chat-android-client/src/main/java/io/getstream/chat/android/client/parser2/...	Removes the dedicated downstream adapter. Direct reaction parsing now requires created_at, updated_at, and user.
Reaction fixtures and validation stream-chat-android-client/src/test/java/io/getstream/chat/android/client/...	Updates reaction fixtures and tests to use ReactionResponse, required fields, nested users, and custom-field shadowing coverage.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Refactor

Suggested reviewers: velikovpetar

Merge Risk: 🔵 Low · up to b87e9

Adding these focused tests would protect the reaction parsing contract against accidental regression.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 23.08% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 13 functions across 11 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the primary change: migrating reaction events and the response wrapper to the generated ReactionResponse.
Description check	✅ Passed	The description clearly covers the goal, implementation, required-field changes, fixture updates, and testing. UI and GIF sections are not relevant because this is a non-UI change.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
In
`@stream-chat-android-client/src/test/java/io/getstream/chat/android/client/parser2/ReactionParsingTest.kt`:
- Line 67: Add direct-path failure tests in ReactionParsingTest for missing
created_at, updated_at, and user fields, using ReactionAdapter/ReactionResponse
parsing and matching the existing missing-field test style. Verify each case
fails while preserving the current tests for message_id, type, score, and
user_id.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Advanced

Run ID: 00264c1a-1b8a-48fe-b569-2cd7411fc677

📥 Commits

Reviewing files that changed from the base of the PR and between 297ba0b and b87e955.

📒 Files selected for processing (20)

• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/ChatClient.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/api2/mapping/DomainMapping.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/api2/model/dto/DownstreamReactionDto.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/api2/model/dto/EventDtos.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/api2/model/response/ReactionResponse.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/parser2/MoshiChatParser.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/parser2/adapters/UpstreamReactionDtoAdapter.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/parser2/direct/ReactionAdapter.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/EventChatJsonProvider.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/Mother.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/api2/MoshiChatApiTestArguments.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/api2/mapping/DomainMappingTest.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/api2/mapping/EventMappingTestArguments.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/parser/EventArguments.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/parser2/DownstreamReactionDtoAdapterTest.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/parser2/ReactionParsingTest.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/parser2/ReactionResponseParsingTest.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/parser2/UpstreamReactionDtoAdapterTest.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/parser2/testdata/ReactionDtoTestData.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/parser2/testdata/ReactionTestData.kt

💤 Files with no reviewable changes (9)

• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/parser2/MoshiChatParser.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/parser2/testdata/ReactionDtoTestData.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/api2/model/dto/DownstreamReactionDto.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/ChatClient.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/parser2/DownstreamReactionDtoAdapterTest.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/parser2/adapters/UpstreamReactionDtoAdapter.kt
• stream-chat-android-client/src/main/java/io/getstream/chat/android/client/api2/mapping/DomainMapping.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/api2/mapping/DomainMappingTest.kt
• stream-chat-android-client/src/test/java/io/getstream/chat/android/client/Mother.kt

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[andremion]

Looks good. Two nits inline, both optional.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud