feat(core): support MIDSCENE_CUSTOM_SYSTEM_PROMPT env var for custom system prompt injection#2488
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feat(core): support MIDSCENE_CUSTOM_SYSTEM_PROMPT env var for custom system prompt injection#2488will- wants to merge 3 commits into
will- wants to merge 3 commits into
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…system prompt injection Allow private/self-hosted models to receive model-specific system prompt instructions via the MIDSCENE_CUSTOM_SYSTEM_PROMPT environment variable. When set, the value is prepended to all system messages across all AI call paths (planning, locate, extract, assert). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Mock the OpenAI client and verify that the custom system prompt is actually prepended to system messages in the API call payload, covering the full callAI → OpenAI path with multimodal and multi-intent scenarios. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
…EM_PROMPT_EXTRA Rename the env var to better communicate its prepend behavior — "extra" makes it clear that this is additional content prepended to the existing system prompt, not a replacement. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
MIDSCENE_CUSTOM_SYSTEM_PROMPTenvironment variable support that prepends a custom system prompt to all AI calls (planning, locate, extract, assert)callAI()entry point, covering all downstream paths including CodexAppServerMotivation
When using private or self-hosted models, some require specific system prompt instructions (e.g., role definitions, output format constraints) that differ from Midscene's built-in prompts. Currently there is no way to inject custom system-level instructions without modifying source code.
This change allows users to simply set an environment variable:
Changes
packages/shared/src/env/types.ts— DeclareMIDSCENE_CUSTOM_SYSTEM_PROMPTconstant and register inSTRING_ENV_KEYSpackages/core/src/ai-model/service-caller/index.ts— AddapplyCustomSystemPrompt()function and call it atcallAI()entry pointpackages/core/tests/unit-test/custom-system-prompt.test.ts— 8 unit tests for the pure functionpackages/core/tests/unit-test/custom-system-prompt-integration.test.ts— 4 integration tests mocking OpenAI client to verify end-to-end behaviorTest plan
pnpm run lint— passes (no new lint errors)vitest --run tests/unit-test/custom-system-prompt.test.ts— 8 passedvitest --run tests/unit-test/custom-system-prompt-integration.test.ts— 4 passed🤖 Generated with Claude Code