RFC: support Junie by JetBrains in lemonade launch

[mashan555]

Proposal size

Minor feature (a single PR)

Updates

No response

User story

As a Junie user, I want lemonade launch junie --model <name> to configure Junie for my local model in one step, so that my code never leaves my machine and I don't burn subscription quota on routine tasks. Today this is painful because, while Junie can already talk to OpenAI-compatible endpoints, the whole setup of local model is manual and I have to redo it whenever I switch models.

High-level design

The lemonade launch command now supports Junie as an agent: lemonade launch junie --model <name>. No new CLI options were added. junie is a new value for the existing AGENT argument, and --model, --api-key, and --agent-args work the same way as with other supported agents. When launched, Lemonade loads the selected model, creates a Junie model profile pointing to Lemonade's OpenAI-compatible endpoint, and starts Junie with that profile. The profile is stored in ~/.junie/models/lemonade.json, or under $JUNIE_HOME if that variable is set. Existing Junie profiles are left untouched. Running the command with a different --model value updates the Lemonade profile for that model. If --model is omitted, Lemonade uses the same interactive model picker as for other agents. The profile contains the API key passed through --api-key, or the default Lemonade placeholder if none is provided, as well as the loaded model's ctx_size. Junie itself is not bundled with Lemonade. If it is not installed, the command prints installation instructions. The integration does not require any server-side, GUI, installer, or packaging changes. Junie is also included in the lemonade launch help output and integration documentation.

Breaking changes

None. junie is a new value for an existing argument.

Maintenance plan

The feature is covered by CI and should not require continuous human intervention. Six tests in test/server_cli2.py use a stub Junie binary, so CI does not depend on a real Junie installation or inference backend. On Linux and macOS, they cover launch arguments, profile generation, --api-key, $JUNIE_HOME, and preservation of existing profiles. On Windows, CI verifies that binary lookup resolves the expected junie.bat shim. The main maintenance risk is upstream changes to Junie's profile format, custom: model syntax, or installer layout. CI verifies what Lemonade generates, but not compatibility with future Junie releases. If one of these integration points changes, the profile writer and its tests will need an update, and I will submit that fix. No version pinning or continuous release tracking is required. For this PR, one manual end-to-end test with a real Junie installation is recommended. A Windows check is also useful because CI only validates the expected shim name against a stub.

Risks

No response

[mashan555]

@bitgamma you're listed as the code owner for the lemonade CLI, so tagging you here. This is a minor feature: adding Junie by JetBrains to lemonade launch, one PR. Would appreciate your take when you have time:)

[bitgamma]

sounds reasonable to me, I would also like to hear @sawansri since agent launch is his area

[sawansri]

This would be a welcome contribution! Please open a PR and request me as a reviewer.

[superm1]

🍋

[jeremyfowers]

🍋

[mashan555]

Created PR here #3621