fix: anchor tool schema messages to English

[mason5052]

Summary

Hard-codes the user-facing description text in the tool JSON schema to English so the LLM never sees the legacy "in user's language only" hint. This stops Russian/mixed-language message and result fields from leaking into traces and the UI when a flow is created in English.

Problem

backend/pkg/tools/args.go declared jsonschema_description tags that told the model to answer "in user's language only" / "in the user's language only" / "in the user's language". Because the schema is reflected once at startup and shared across flows, a flow in English would still receive the Russian-leaning hint baked into the tool definitions, producing the mixed-language tool-call output reported in #285.

Solution

Replace every in user's language only, in the user's language only, and in the user's language occurrence with in English in the struct tags across backend/pkg/tools/args.go. The follow-up commit also removed the remaining in the user's language (without "only") schema hints on the search action Message fields, so no schema description still instructs the model to answer in the user's language. No runtime locale logic, no schema re-shape, no API/DB/UI change.

User Impact

• New flows: tool-call message / result / clarification fields render in English regardless of UI locale.
• No migration, config, or restart steps for users.
• Flow.language is unchanged; if multilingual support is added later, this is a one-line edit per field.

Test Plan

• TestToolSchemasDoNotInstructUsersLanguage sweeps every tool returned by GetRegistryDefinitions() and fails if any of the broader forbidden patterns (user's language, the user's language) reappear in any tool schema, not just the old exact user's language only phrase.
• TestUserFacingMessageDescriptionsAreEnglishAnchored asserts the eight user-facing message/result properties carry the "in English" anchor, going through the same reflector.Reflect path the LLM sees.
• go test ./pkg/tools/... passes locally.
• rg "user's language|the user's language" backend/pkg/tools/args.go returns no matches (verified).

Closes #285

[Copilot]

Pull request overview

This PR removes locale-ambiguous “in user's language only” hints from tool argument JSON schema descriptions and replaces them with an explicit “in English” anchor, preventing mixed-language tool-call message/result outputs (per #285).

Changes:

• Updated jsonschema_description struct tags in backend/pkg/tools/args.go to replace “in user's language only” with “in English” for user-facing message/result fields.
• Added regression tests to ensure tool schemas never reintroduce the banned substring and that key message/result descriptions explicitly include “in English”.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
backend/pkg/tools/args.go	Re-anchors user-facing tool schema descriptions from “user’s language only” to “in English”.
backend/pkg/tools/args_test.go	Adds regression tests to prevent reintroduction of locale-ambiguous schema text and assert English anchoring for key fields.

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[mason5052]

Pushed a follow-up (7437520) that broadens the regression guard.

Previously the test only checked for the literal substring "user's language only". The schema also had two other "in the user's language" variants that weren't directly caught by the guard. The test now iterates over a forbidden-pattern slice ("user's language", "the user's language") and fails on any of them, so any future drift -- with or without the leading article, with or without "only" -- is caught the same way.

Renamed the test to TestToolSchemasDoNotInstructUsersLanguage to reflect the broader contract. go test ./pkg/tools/... is green.

[mason5052]

PR body refreshed to reflect the follow-up commit (7437520).

The earlier body said three in the user's language (without "only") strings on the search action Message fields were intentionally left alone. That is no longer accurate — the follow-up removed those three remaining hints as well, and the regression test was broadened to reject user's language and the user's language (not only user's language only).

rg "user's language|the user's language" backend/pkg/tools/args.go now returns no matches, so no schema description still instructs the model to answer in the user's language.