Inject shared chat mode notices

[TraderSamwise]

Summary

• inject an agent-facing note when a shared chat enters multi-user mode
• inject a downgrade note when the same shared chat returns to single-user mode
• keep persisted chat history as the original human messages while only changing agent-bound input

Verification

• yarn vitest run src/multiplexer/session-runtime-core.test.ts src/collaboration.test.ts
• yarn typecheck
• yarn build

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Improved handling of collaboration context when transitioning between multi-user and single-user modes.
  • Enhanced message formatting and metadata preservation during mode switches.

• Tests

  • Expanded test coverage for multi-user mode transitions and message storage.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR updates writeAgentInput to inject collaboration-mode notices into agent input before serialization, with per-session deduping to prevent redundant notices. Two new helpers handle notice generation and merging with the input shape. The test is extended to validate notice text and formatting changes across multi→multi→single mode transitions.

Changes

Collaboration-mode notice injection

Layer / File(s)	Summary
Collaboration-mode notice infrastructure src/multiplexer/session-runtime-core.ts	Imports AgentInputPart type and adds consumeCollaborationModeNotice (generates a mode-change notice when collaboration.shareId and collaboration.mode are set, deduping per session and shareId:mode pair) and applyCollaborationContextForAgent (prepends notice to parts if present, otherwise prefixes data).
writeAgentInput integration src/multiplexer/session-runtime-core.ts	writeAgentInput now calls applyCollaborationContextForAgent to conditionally inject collaboration-mode notices based on the incoming collaboration object and session deduping state, replacing the previous prefix-only approach.
Mode transition test coverage src/multiplexer/session-runtime-core.test.ts	Test extended to submit two additional writeAgentInput calls (one in multi mode, one switching to single) and validates that collaboration-note prefixes, message formatting, chatMode, and clientMessageId values match the expected sequence across the multi→multi→single transition.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• TraderSamwise/aimux#21: Wires trusted header parsing/stripping that produces the collaboration context object that this PR injects into agent input.
• TraderSamwise/aimux#18: Establishes the ShareChatMode upgrade/downgrade and message prefixing rules that this PR's collaboration-mode notice injection implements.

Poem

🐰 A notice now whispers when modes align,
Multi speaks to single through the design,
Sessions remember, no repeat refrain,
Input flows richer through the agent's domain! 🎯

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Inject shared chat mode notices' directly and specifically describes the main change in both modified files—adding collaboration mode context injection to agent input in the runtime core and extending tests to validate this behavior.
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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✨ 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/multi-user-chat-agent-context

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[coderabbitai]

🧹 Nitpick comments (1)

src/multiplexer/session-runtime-core.test.ts (1)

206-260: ⚡ Quick win

Consider adding test coverage for single→multi transition and shareId switching.

The current test validates multi→multi(dedupe)→single, which covers the core functionality. To ensure robustness, consider adding test cases for:

1. single→multi transition: Start in single mode then upgrade to multi mode to verify the upgrade notice.
2. ShareId switching: Write with share_A→share_B→share_A to confirm the deduping behavior when switching conversation contexts.

These additions would validate edge cases but are not critical for the current implementation.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/multiplexer/session-runtime-core.test.ts` around lines 206 - 260, Add two
focused test cases in session-runtime-core.test.ts: one for single→multi
transition and one for shareId switching. For the single→multi test, use
writeAgentInput to send an initial message with mode "single" (e.g., client-1),
then send another with mode "multi" and the same shareId (e.g., client-2) and
assert writes contains the "Aimux collaboration note" upgrade message and both
messages are recorded via readSessionMessages with correct chatMode values. For
the shareId switching test, call writeAgentInput with shareId "share_A", then
"share_B", then "share_A" again and assert writes and readSessionMessages
reflect deduping/notice behavior when switching shareId (verify messages keep
correct shareId fields and ordering). Use the existing helpers writeAgentInput,
readSessionMessages and the writes array and expect(...) assertions to mirror
the style of the surrounding tests.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@src/multiplexer/session-runtime-core.test.ts`:
- Around line 206-260: Add two focused test cases in
session-runtime-core.test.ts: one for single→multi transition and one for
shareId switching. For the single→multi test, use writeAgentInput to send an
initial message with mode "single" (e.g., client-1), then send another with mode
"multi" and the same shareId (e.g., client-2) and assert writes contains the
"Aimux collaboration note" upgrade message and both messages are recorded via
readSessionMessages with correct chatMode values. For the shareId switching
test, call writeAgentInput with shareId "share_A", then "share_B", then
"share_A" again and assert writes and readSessionMessages reflect
deduping/notice behavior when switching shareId (verify messages keep correct
shareId fields and ordering). Use the existing helpers writeAgentInput,
readSessionMessages and the writes array and expect(...) assertions to mirror
the style of the surrounding tests.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: c7b9e1c1-ba59-44e6-bfb8-7f5c3e250d97

📥 Commits

Reviewing files that changed from the base of the PR and between e420233 and c14d5c0.

📒 Files selected for processing (2)

• src/multiplexer/session-runtime-core.test.ts
• src/multiplexer/session-runtime-core.ts