feat(adapters): add LangChain export adapter & runner with multi-provider support

[AJAmit17]

Summary

This is a clean rebase of #16 onto current main. The original PR predated several merges that touched the same integration files (src/adapters/index.ts, src/commands/export.ts, src/commands/run.ts), making the diff unreadable. This branch is three focused commits on top of b3a057a with all conflicts resolved — no existing adapters or options were removed.

Original PR: #16 (superseded by this one — closed)
Closes: #2

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Hey @shreyas-lyzr — this is the clean rebase you asked for. Quick summary of what changed since #16:

• Rebased onto current main (b3a057a) as a single feature commit — no merge noise
• All integration files (src/adapters/index.ts, src/commands/export.ts, src/commands/run.ts) updated additively — kiro, gitclaw, --workspace, and exportToClaudeCodeString are all intact
• Both reviewer questions from feat(langchain): add LangChain export adapter & runner with multi-provider support #16 answered inline below (runner scope + provider precedence)
• Also picked up and fixed the pre-existing TypeScript build failure from feat: financial_governance spec block — Phase 1 (schema + example) #79 so CI goes green (details in the section below)

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What this adds

LangChain as a first-class export + run target alongside the existing adapters (kiro, gitclaw, codex, etc.):

File	Role
src/adapters/langchain.ts	Converts agent.yaml → standalone Python script using LangChain agent framework
src/runners/langchain.ts	Executes the generated script in an auto-managed Python venv at ~/.gitagent/langchain-venv
src/adapters/langchain.test.ts	Unit tests for provider detection and export shape
docs/adapters/langchain.md	Full field-mapping table, provider table, usage examples

Integration changes (additive only):

• src/adapters/index.ts — exportToLangChain added as a new export line
• src/commands/export.ts — langchain case added; format help string updated
• src/commands/run.ts — langchain case added; adapter help string updated

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Also fixes: pre-existing TypeScript build failure from #79

PR #79 added financial_governance references in src/commands/validate.ts and src/adapters/shared.ts but the property was never declared on ComplianceConfig in src/utils/loader.ts, causing a TypeScript build failure on all Node versions in CI. This PR adds the missing type declaration and guards the unsafe <= 0 comparison that the strict types exposed.

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Addressing reviewer questions from #16

Q: Is runWithLangChain invoking the user's installed Python LangChain (subprocess) or shipping a JS LangChain runtime?

Subprocess. The runner (src/runners/langchain.ts) bootstraps a Python venv at ~/.gitagent/langchain-venv on first run, installs the required langchain-openai or langchain-anthropic pip package depending on the detected provider, writes the generated Python script to a temp file, then invokes it via spawnSync. No JS LangChain runtime is shipped.

Q: Multi-provider switching — provider precedence and conflict behaviour?

Provider is determined solely from manifest.model.preferred (the model name string). The detection rules:

• claude-* → Anthropic (langchain-anthropic, ANTHROPIC_API_KEY)
• gpt-*, o1-*/o2-*/o3-*/o4-* → OpenAI (langchain-openai, OPENAI_API_KEY)
• Anything else → hard error at export time (unsupported model)

The corresponding env var must be set at runtime; the runner validates and errors clearly if it is missing. There is no silent fallback between providers.

Q: Fidelity matrix row?

Happy to add a row to paper/tables/fidelity-matrix.csv in a follow-up, or I can include it here if preferred — just say the word.

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Note on scope vs #80 (LangGraph + DeepAgents)

PR #80 added LangGraph (the state-machine layer on top of LangChain) and DeepAgents (a higher-level harness). This PR adds the base LangChain runtime. They compose — LangGraph imports from LangChain — so this is the foundational piece, not a duplicate.

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Test plan

• npm run build passes (Node 18 / 20 / 22)
• gitagent export --format langchain -d <agent-dir> produces a valid Python script
• gitagent run -a langchain -d <agent-dir> -p "hello" bootstraps venv and executes
• Provider detection unit tests pass (langchain.test.ts)
• Manually validated on Windows 11, Node 22, Python 3.12 with OpenAI and Anthropic models
• All existing adapter cases untouched (kiro, gitclaw, codex, cursor, gemini, etc.)
• ComplianceConfig type fix unblocks CI for all open PRs targeting main