fix: harden reasoning effort state handling

.brv/context-tree/facts/preference/reasoning_effort.md

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+---
+title: Reasoning Effort
+summary: Reasoning effort preference is set to low.
+tags: []
+related: []
+keywords: []
+createdAt: '2026-04-25T10:20:14.913Z'
+updatedAt: '2026-04-25T11:55:01.662Z'
+---
+## Reason
+User set the reasoning effort preference to low.
+
+## Raw Concept
+**Task:**
+Record the user's reasoning effort preference
+
+**Changes:**
+- Set reasoning effort to low
+- Confirmed the setting is set to low
+- Clarified that the low setting persists beyond a single turn until explicitly changed again
+- Set reasoning effort to medium
+- User set reasoning effort to low
+- Assistant confirmed it was not persisted
+- Set thinking level to low without persisting it
+- Reasoning effort set to low
+- Captured instruction to actively manage reasoning effort
+
+**Flow:**
+User preference stated -> preference recorded
+
+**Timestamp:** 2026-04-25
+
+**Author:** user
+
+## Narrative
+### Structure
+A simple preference entry under facts/preference.
+
+### Dependencies
+Applies when deciding how much internal reasoning to use for the current turn.
+
+### Highlights
+The user explicitly set reasoning effort to low.
+
+## Facts
+- **reasoning_effort**: Reasoning effort is set to low [preference]
+
+---
+
+## Cross-reference notes
+- This entry is the canonical source for the reasoning effort preference.
+- The abstract and overview files are derivative summaries and should point here if retained.

.brv/context-tree/facts/project/reasoning_effort_behavior.md

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+---
+title: Reasoning Effort Behavior
+summary: Temporary low reasoning effort can be set in a live session, invalid levels are rejected, and the next idle transition should reset to medium once.
+tags: []
+related: []
+keywords: []
+createdAt: '2026-04-25T11:53:01.433Z'
+updatedAt: '2026-04-25T11:54:28.539Z'
+---
+## Reason
+Persist lasting knowledge about reasoning effort behavior, validation, and checks
+
+## Raw Concept
+**Task:**
+Document reasoning effort session behavior and verification outcomes
+
+**Changes:**
+- Split state into currentVariant, persistedVariant, and temporaryResetVariant
+- Temporary reasoning effort now resets only once on session.idle
+- Reset prompts are ignored so they do not remain visible in-context
+- Persisted reasoning effort no longer triggers idle reset
+- Invalid levels are rejected before calling promptAsync or mutating state
+- System guidance now uses the transform hook model variants for new sessions
+- System prompt guidance is now one consolidated entry
+- Removed v2 SDK type imports and @ts-expect-error usage around variant
+- Set temporary reasoning effort to low
+- Confirmed invalid reasoning effort level is rejected before mutation
+- Observed expected one-time idle reset behavior to medium
+- Verified tests, typecheck, lint, format:check, and build passed
+
+**Files:**
+- src/index.ts
+- src/index.test.ts
+
+**Flow:**
+set reasoning effort -> validate level -> run checks -> idle transition resets to medium once
+
+**Timestamp:** 2026-04-25T11:54:23.547Z
+
+**Author:** assistant
+
+## Narrative
+### Structure
+This entry records a live-session reasoning-effort state change and the expected follow-up idle reset behavior.
+
+### Dependencies
+The behavior depends on the session state machine and validation for allowed reasoning effort levels.
+
+### Highlights
+A temporary low setting was accepted, an invalid level was rejected, and the next idle transition should restore medium only once.
+
+### Rules
+Temporary reasoning effort now resets only once on session.idle. Reset prompts are ignored and should not remain visible in-context. Invalid levels are rejected before calling promptAsync or mutating state.
+
+### Examples
+Checks that passed included pnpm run test, pnpm run typecheck, pnpm run lint, pnpm run format:check, and pnpm run build.
+
+## Facts
+- **reasoning_effort**: Reasoning effort was set to low in a live session. [project]
+- **reasoning_effort_validation**: Invalid reasoning effort levels are rejected before mutation. [project]
+- **reasoning_effort_reset_behavior**: The temporary low reasoning effort should reset to medium once on idle, then stop repeating. [project]
+- **verification_status**: Automated checks passed: test, typecheck, lint, format:check, and build. [project]

.brv/context-tree/facts/project/reasoning_effort_confirmation.md

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+---
+title: Reasoning Effort Confirmation
+summary: The only visible confirmation after the tool call was "Reasoning effort set to low".
+tags: []
+related: []
+keywords: []
+createdAt: '2026-04-25T11:06:39.753Z'
+updatedAt: '2026-04-25T11:08:43.379Z'
+---
+## Reason
+Preserve the confirmed visible tool output from the conversation.
+
+## Raw Concept
+**Task:**
+Document the visible confirmation message related to reasoning effort.
+
+**Changes:**
+- Recorded the exact confirmation text that was visible in the conversation
+- Captured the confirmation text shown after the tool call.
+
+**Flow:**
+tool call -> visible confirmation -> observation recorded
+
+**Timestamp:** 2026-04-25
+
+## Narrative
+### Structure
+A single confirmation message was observed in the chat.
+
+### Highlights
+No separate reset message was visible; only "Reasoning effort set to low" appeared.
+
+## Facts
+- **reasoning_effort_confirmation**: The only visible confirmation after the tool call was "Reasoning effort set to low". [project]

.brv/context-tree/facts/project/reasoning_effort_reset_behavior.md

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+---
+title: Reasoning Effort Reset Behavior
+summary: Reasoning effort can be reset to medium, and the reset notice states that it has been reset to medium.
+tags: []
+related: []
+keywords: []
+createdAt: '2026-04-25T11:09:11.082Z'
+updatedAt: '2026-04-25T11:54:47.414Z'
+---
+## Reason
+Document persistent reasoning effort reset behavior from conversation
+
+## Raw Concept
+**Task:**
+Document reasoning effort reset behavior
+
+**Changes:**
+- Added set_reasoning_effort tool for session variant control
+- Implemented session.idle reset attempt based on cached variant
+- Observed undefined priorState.variant in the reset prompt body
+- Reset notice indicates reasoning effort reset to medium
+
+**Files:**
+- src/index.ts
+
+**Flow:**
+reset notice -> reasoning effort set to medium
+
+**Timestamp:** 2026-04-25
+
+## Narrative
+### Structure
+The note records a reset-state confirmation for reasoning effort.
+
+### Dependencies
+Depends on client.session.messages, client.app.agents, and client.session.promptAsync for variant resolution and state changes.
+
+### Highlights
+The reset notice explicitly says: Reasoning effort reset to medium.
+
+## Facts
+- **reasoning_effort_reset**: Reasoning effort was reset to medium. [project]

.brv/context-tree/facts/project/reasoning_effort_reset_message.md

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+---
+title: Reasoning Effort Reset Message
+summary: Reasoning effort was reset to medium, with no separate tool-generated reset confirmation observed beyond an earlier low setting message.
+tags: []
+related: []
+keywords: []
+createdAt: '2026-04-25T11:08:33.219Z'
+updatedAt: '2026-04-25T11:11:38.940Z'
+---
+## Reason
+Persist the observed reset message and prior state from the conversation.
+
+## Raw Concept
+**Task:**
+Document reasoning effort reset message behavior observed in conversation
+
+**Changes:**
+- Captured the only visible reset-related message from the conversation
+- Observed a reset message indicating reasoning effort reset to medium
+- Noted there was no separate tool-generated reset confirmation
+
+**Flow:**
+user asks about reset message -> assistant confirms message content -> assistant notes lack of separate tool-generated confirmation
+
+**Timestamp:** 2026-04-25T11:11:28.548Z
+
+## Narrative
+### Structure
+The conversation centers on whether a reset message is visible and what it says.
+
+### Dependencies
+The assistant distinguishes between the user-visible reset message and a separate tool-generated confirmation.
+
+### Highlights
+The reset message states medium, and the assistant references an earlier low setting message as prior context.
+
+## Facts
+- **reasoning_effort**: Reasoning effort reset to medium. [project]
+- **reasoning_effort**: An earlier message said reasoning effort was set to low. [project]

.brv/context-tree/facts/project/reasoning_effort_reset_notice.md

@@ -0,0 +1,36 @@
+---
+title: Reasoning Effort Reset Notice
+summary: Reasoning effort reset notice is visible and states that reasoning effort reset to medium.
+tags: []
+related: []
+keywords: []
+createdAt: '2026-04-25T11:44:48.223Z'
+updatedAt: '2026-04-25T11:44:48.223Z'
+---
+## Reason
+Capture lasting project behavior about reasoning effort reset notice visibility
+
+## Raw Concept
+**Task:**
+Document the observed reasoning effort reset notice and message
+
+**Changes:**
+- Confirmed the reset notice is visible
+- Recorded the reset message as medium
+
+**Flow:**
+user asks about reset -> assistant confirms visible notice -> message indicates medium reset
+
+## Narrative
+### Structure
+A brief exchange confirming the presence of a reasoning effort reset notice and its displayed message.
+
+### Highlights
+The notice is visible and explicitly reports a reset to medium.
+
+### Examples
+User asked, "And do you see the reset?" and the assistant replied that it saw the reset notice.
+
+## Facts
+- **reasoning_effort_reset_notice_visibility**: A reasoning effort reset notice is visible. [project]
+- **reasoning_effort_reset_message**: The reset notice says "Reasoning effort reset to medium." [project]

.brv/context-tree/facts/project/reasoning_effort_reset_notice_visibility.md

@@ -0,0 +1,33 @@
+---
+title: Reasoning Effort Reset Notice Visibility
+summary: The reset notice is visible as a user-level message rather than a separate tool confirmation.
+tags: []
+related: []
+keywords: []
+createdAt: '2026-04-25T11:12:05.181Z'
+updatedAt: '2026-04-25T11:12:05.181Z'
+---
+## Reason
+Capture lasting note about reset notice being visible to the user
+
+## Raw Concept
+**Task:**
+Document the visibility of the reasoning effort reset notice
+
+**Changes:**
+- Confirmed the reset notice appears as a user-level message
+
+**Flow:**
+reset action -> notice displayed -> user sees confirmation message
+
+**Timestamp:** 2026-04-25T11:12:01.205Z
+
+## Narrative
+### Structure
+A brief confirmation that the reset notice is exposed directly to the user in chat.
+
+### Highlights
+The assistant explicitly confirmed the reset notice is not a separate tool confirmation.
+
+## Facts
+- **reset_notice_visibility**: The reset notice is visible as a user-level message rather than a separate tool confirmation. [project]

.brv/context-tree/facts/project/reasoning_effort_state_handling.md

@@ -0,0 +1,31 @@
+---
+title: Reasoning Effort State Handling
+summary: x
+tags: []
+related: []
+keywords: []
+createdAt: '2026-04-25T11:48:50.291Z'
+updatedAt: '2026-04-25T11:48:50.291Z'
+---
+## Reason
+x
+
+## Raw Concept
+**Task:**
+x
+
+**Changes:**
+- x
+
+**Flow:**
+x
+
+## Narrative
+### Structure
+x
+
+### Dependencies
+x
+
+### Highlights
+x

.changeset/clean-ravens-reset.md

@@ -0,0 +1,5 @@
+---
+"opencode-adaptive-thinking": patch
+---
+
+Harden reasoning effort state handling so temporary settings reset once, persisted settings do not reset on idle, invalid levels are rejected before mutation, and system guidance is added as one consolidated prompt entry.