port(go): Cursor PS 5.1 bridge shell guidance (#627 / #604)

[Wibias]

Summary

Defer the Go port of #627 (dcaede6e on dev; carried to dev2-go via the sync PR).

TS changed Cursor native-shell denial text and tool-guidance system notes so Windows PowerShell 5.1 bridge attempts stop looping (&&/||, cd /d, heredocs; at most one corrected retry).

Go counterpart

• go/internal/adapter/cursor/tool_defs.go — BuildToolGuidance (and related CursorShellAliasSystemNote / CursorShellAliasUserHint) need the same host-shell-neutral PS 5.1 + one-retry-stop guidance.
• Policy denial UX for Cursor-native shell (if/when Go surfaces a model-facing steer message like TS nativeShellDisabledMessage) should stay aligned.

Source commits

• dev: dcaede6e — fix(cursor): steer Windows bridge shell away from PS 5.1 syntax loops (fix(cursor): steer Windows bridge shell away from PS 5.1 syntax loops #627)
• Pre-squash tip commits (for history): 2611629e, b5d5bc52, bacda33e

Tracking

Closes nothing until the Go strings/guidance match #604 / #627 behavior on dev2-go.

[github-actions]

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