Implement steering messages — interrupt and redirect while processing

[PureWeen]

What

When a user sends a message while the assistant is still processing, PolyPilot now supports steering messages — the ability to interrupt and redirect the conversation in a new direction.

How

Hybrid steering strategy

Two steering modes based on session state:

Soft steer (agentic/tool-heavy sessions):

• Triggered when ActiveToolCallCount > 0 || HasUsedToolsThisTurn
• Uses Mode = "immediate" via the Copilot SDK to inject the steering message into the current turn
• Maps to the CLI's ImmediatePromptProcessor.addMessage() — no abort, no context loss
• Preserves tool call history and conversation context

Hard steer (plain streaming):

• Triggered when no tools are/were active
• Calls AbortSessionAsync(markAsInterrupted: true) then starts a new turn
• Immediate interruption; partial response marked with IsInterrupted = true

Demo and Remote sessions skip soft steer (no real CopilotSession) and fall through to hard steer.

Key changes

• ChatMessage.IsInterrupted — new bool property on PolyPilot's custom ChatMessage model; set on partial responses when interrupted
• SteerSessionAsync in CopilotService.cs — new method implementing the hybrid strategy
• ProcessingGeneration guard in SendPromptAsync catch block — prevents SendingFlag being clobbered by an old turn's cleanup after abort+restart
• UI placeholder — shows Send to steer… in ExpandedSessionView during processing
• Dashboard.razor — routes to SteerSessionAsync instead of EnqueueMessage when IsProcessing=true

Testing

17 new tests in SteeringMessageTests.cs covering:

• Hard steer path (plain streaming)
• Soft steer path (tools active, tools used this turn)
• Demo mode bypass
• Generation guard (no double SendingFlag reset)
• IsInterrupted flag set on partial responses

Research notes

Investigated how the Copilot CLI implements steering:

• CLI uses send({ mode: "immediate" }) to inject steering into current turn without aborting
• .NET SDK wires MessageOptions.Mode through RPC to JS LocalSession.send({ mode })
• agentMode in JS comes from session state, not the RPC mode field — confirmed safe to use Mode for routing
• PR Fix agent mode routing -- stop overloading MessageOptions.Mode #232 (merged) cleaned up the prior misuse of Mode for agent modes

Closes #231

[PureWeen]

PR #271 Re-Review: Steering Messages

5-model consensus review (claude-opus-4.6 ×2, claude-sonnet-4.6, gemini-3-pro-preview, gpt-5.3-codex) of the full diff including the prior fix commit cd2d498.

CI status: ⚠️ No checks reported on steering-hybrid branch (pre-existing: 13 PopupThemeTests failures unrelated to this PR).

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Previous Findings — All Fixed ✅

Finding	Status
P1: SendingFlag not released in soft steer catch → session deadlock	✅ FIXED (Interlocked.Exchange added)
P2: ResponseCompletion TCS orphaned in soft steer catch → task leak	✅ FIXED (TrySetCanceled() added)
P3: SteerSessionAsync no IsProcessing guard	✅ FIXED (check present)

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Remaining Findings (Consensus Filter: 2+ models)

🟡 MODERATE — CopilotService.cs:2333 — Soft steer error path missing queue cleanup (2/4 models)

The soft steer catch block cleared IsProcessing, SendingFlag, and companion fields — but was missing the same queue cleanup that AbortSessionAsync performs:

// Missing from soft steer catch (AbortSessionAsync does all of these):
state.Info.MessageQueue.Clear();
_queuedImagePaths.TryRemove(sessionName, out _);
_queuedAgentModes.TryRemove(sessionName, out _);
state.FlushedResponse.Clear();
state.PendingReasoningMessages.Clear();

Stale queue entries would persist and auto-send after the next successful turn completes. Fixed in commit 542fda3.

🟢 MINOR — CopilotService.cs:1951 — myGeneration = 0 is a silent-failure sentinel (3/4 models)

myGeneration is initialized to 0 outside the try block, then set to the return of Interlocked.Increment as the 5th statement inside try. The four statements before the increment are simple property assignments that cannot throw. However, if the initialization order ever changes and an early throw occurs before the increment, myGeneration stays 0, the generation guard 0 != actual_generation fails, and SendingFlag is never released — permanent session deadlock. Recommend moving the increment to be the very first statement inside the try block (or use long.MinValue as sentinel), to make the guard fail-loud instead of fail-silent.

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Test Coverage

New SteeringMessageTests.cs (353 lines, 19 tests) covers: IsInterrupted model property, abort with/without mark, SteerSessionAsync idle/processing/tool paths, fire-and-forget safety, history persistence, and lock-guard regression. Coverage is thorough for the hard steer path. The soft steer path is (correctly) not unit-testable without a live SDK session — the SteerSession_SoftSteerPath_ContainsUserMessageAddition test compensates by validating source structure via reflection.

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Commits on branch

• 831215c feat: implement steering messages
• 6ea1bd0 fix: guard SendingFlag release by generation in catch block
• 10e1d6e fix: address race conditions and missing history
• cd03d76 feat: hybrid steering — soft steer via Mode=immediate when tools active
• cfe1043 fix: add try/catch around soft steer SendAsync
• cd2d498 fix: release SendingFlag and signal ResponseCompletion in soft steer catch (prior fix)
• 542fda3 fix: clear MessageQueue, FlushedResponse, PendingReasoningMessages in soft steer error path (this review)

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Recommended Action: ⚠️ Request Changes

One item outstanding: move myGeneration = Interlocked.Increment(...) to be the first statement inside the try block (minor refactor, 5-line change) to eliminate the silent-deadlock risk if initialization order changes. All critical findings are now resolved.