refactor(slack-bot): make app.py a thin composition root

[kevkantes]

Description

Refactors the Slack bot entry point into a thin composition root while preserving existing Slack-visible behavior.

• Moves runtime construction and startup checks into a dedicated bootstrap module.
• Extracts authorization, conversation, channel routing, personal routing, and action handlers behind narrow dependency views.
• Separates AG-UI event interpretation from Slack formatting and delivery.
• Documents the request path and module ownership.
• Adds import-safety, registration-boundary, bootstrap, routing, and AG-UI characterization tests.

Closes #2422

Type of Change

• Bugfix
• New Feature
• Breaking Change
• Refactor
• Documentation
• Other (please describe)

Temporary Helm Charts (Optional)

For chart changes, you can test temporary versions before merging:

• Base repo contributors: Create a branch starting with prebuild/ for automatic prebuilds
• Fork contributors: Ask a maintainer to add the helm-prerelease label
• Temporary charts are published to ghcr.io/caipe-io/charts with PR-specific versions
• Cleanup happens automatically when the PR closes or label is removed

Checklist

• I have read the contributing guidelines
• Existing issues have been referenced (where applicable)
• I have verified this change is not present in other open pull requests
• Functionality is documented
• All code style checks pass
• New code contribution is covered by automated tests
• All new and existing tests pass

[github-actions]

ℹ️ Branch is behind main (advisory, non-blocking)

Commit: 35ff09b2

This branch does not yet contain the latest main. This does not fail the version-bump check — version files are bumped once the branch is updated, and GitHub branch protection still requires the branch to be up to date before merge. Use the Update branch button on this PR, or run:

git fetch origin main
git checkout prebuild/refactor/slack-composition-root
git merge FETCH_HEAD
git push

This is a prebuild/* branch, so Helm prebuild publishing will still run so you can test the chart changes while the branch is being updated.

[github-actions]

✅ No proprietary content detected. This PR is clear for review!

[caipe-io-ci-release]

Prebuild Artifacts for `35ff09b` (archived)

Prebuild Artifacts for 35ff09b

Branch: prebuild/refactor/slack-composition-root
Commit: 35ff09b

Docker Images

Artifact	Image	Tag	Status	CI
caipe-slack-bot	ghcr.io/caipe-io/caipe-slack-bot	refactor-slack-composition-root-2	Published	CI

Docker pull commands

docker pull ghcr.io/caipe-io/caipe-slack-bot:refactor-slack-composition-root-2

Helm Charts

Chart	Registry	Version	Status	CI
ai-platform-engineering	ghcr.io/caipe-io/charts	1.0.0-dev.6-refactor-slack-composition-root-1	Published	CI
rag-stack	ghcr.io/caipe-io/charts	1.0.0-dev.6-refactor-slack-composition-root-1	Published	CI

Helm install commands

helm upgrade --install ai-platform oci://ghcr.io/caipe-io/charts/ai-platform-engineering --version 1.0.0-dev.6-refactor-slack-composition-root-1
helm upgrade --install rag oci://ghcr.io/caipe-io/charts/rag-stack --version 1.0.0-dev.6-refactor-slack-composition-root-1

These prebuild artifacts will be automatically cleaned up when the PR is closed or merged.

[caipe-io-ci-release]

Prebuild Artifacts for `24ef317` (archived)

Prebuild Artifacts for 24ef317

Branch: prebuild/refactor/slack-composition-root
Commit: 24ef317

Docker Images

Artifact	Image	Tag	Status	CI
caipe-slack-bot	ghcr.io/caipe-io/caipe-slack-bot	refactor-slack-composition-root-3	Published	CI

Docker pull commands

docker pull ghcr.io/caipe-io/caipe-slack-bot:refactor-slack-composition-root-3

These prebuild artifacts will be automatically cleaned up when the PR is closed or merged.

[caipe-io-ci-release]

Prebuild Artifacts for `acb9316` (archived)

Prebuild Artifacts for acb9316

Branch: prebuild/refactor/slack-composition-root
Commit: acb9316

Docker Images

Artifact	Image	Tag	Status	CI
caipe-slack-bot	ghcr.io/caipe-io/caipe-slack-bot	refactor-slack-composition-root-3	Published	CI

Docker pull commands

docker pull ghcr.io/caipe-io/caipe-slack-bot:refactor-slack-composition-root-3

These prebuild artifacts will be automatically cleaned up when the PR is closed or merged.

[caipe-io-ci-release]

Prebuild Artifacts for `0a8d66f` (archived)

Prebuild Artifacts for 0a8d66f

Branch: prebuild/refactor/slack-composition-root
Commit: 0a8d66f

Docker Images

Artifact	Image	Tag	Status	CI
caipe-slack-bot	ghcr.io/caipe-io/caipe-slack-bot	refactor-slack-composition-root-4	Published	CI

Docker pull commands

docker pull ghcr.io/caipe-io/caipe-slack-bot:refactor-slack-composition-root-4

These prebuild artifacts will be automatically cleaned up when the PR is closed or merged.

[caipe-io-ci-release]

Prebuild Artifacts for `4096ae9` (archived)

Prebuild Artifacts for 4096ae9

Branch: prebuild/refactor/slack-composition-root
Commit: 4096ae9

Docker Images

Artifact	Image	Tag	Status	CI
caipe-slack-bot	ghcr.io/caipe-io/caipe-slack-bot	refactor-slack-composition-root-4	Published	CI

Docker pull commands

docker pull ghcr.io/caipe-io/caipe-slack-bot:refactor-slack-composition-root-4

These prebuild artifacts will be automatically cleaned up when the PR is closed or merged.

[caipe-io-ci-release]

Prebuild Artifacts for 4d3d24b

Branch: prebuild/refactor/slack-composition-root
Commit: 4d3d24b

Docker Images

Artifact	Image	Tag	Status	CI
caipe-slack-bot	ghcr.io/caipe-io/caipe-slack-bot	refactor-slack-composition-root-4	Published	CI

Docker pull commands

docker pull ghcr.io/caipe-io/caipe-slack-bot:refactor-slack-composition-root-4

These prebuild artifacts will be automatically cleaned up when the PR is closed or merged.