[waldekmastykarz]

Resolves #2071

Problem

Reporters wrote reports to a relative file name, so they always landed in Dev Proxy's current working directory. Scripts that wanted reports elsewhere had to start Dev Proxy with a different cwd, which also changes how relative config paths and devproxyrc.json discovery resolve.

Changes

• reportsFolder setting in devproxyrc.json. Relative paths resolve against the config file's folder (like other paths in config files); ~/, ~appFolder, and ~dataFolder tokens are supported.
• --report-dir <path> CLI option. Relative paths resolve against the current working directory (standard CLI behavior) and override reportsFolder. Rejects a path that points to an existing file.
• BaseReporter (Json, Markdown, PlainText reporters) writes to that folder and creates it if needed. The existing "file exists → append timestamp" behavior is preserved inside the folder. Default is unchanged: the working directory.
• IProxyConfiguration.ReportsFolder added; BaseReporter gets a new constructor overload taking IProxyConfiguration. The original constructor is kept so third-party reporters keep compiling (they keep writing to the cwd).
• schemas/v4.0.0/rc.schema.json documents reportsFolder.

Scope note

Generator plugins (HAR, mocks, OpenAPI, TypeSpec, .http) also write files to the cwd. I left them out to keep this PR to the reporters the issue calls out; happy to follow up if we want them to honor the same folder.

Testing

• Unit tests for config-relative resolution, absolute paths, unset value, and --report-dir resolution (incl. ~/).
• Integration tests: report written into a (missing, nested) reports folder and not the cwd; timestamp suffix when the file exists; cwd fallback when unset.
• Manual e2e: reportsFolder in config → report lands next to the config file; --report-dir with --detach → report lands relative to the invoking cwd.

[Copilot]

🟢 Approval recommended

No active review issues are recorded for the configurable reporter output-folder change.

No open issues 🎉

What changed in this PR

Adds configurable output folders for Dev Proxy reporters without changing the working directory or config discovery behavior.

Changes:

• Adds reportsFolder and the overriding --report-dir option, with config-relative and working-directory-relative path resolution respectively.
• Updates JSON, Markdown, and plain-text reporters to create and use the selected folder while preserving timestamp suffixes and the default working-directory behavior.
• Adds unit and integration coverage for path resolution and report output.

File	Description
schemas/​v4.0.0/​rc.schema.json	Documents the reportsFolder setting.
DevProxy/​Proxy/​ProxyConfiguration.cs	Resolves configured report paths relative to the config file.
DevProxy/​Commands/​DevProxyCommand.cs	Adds, validates, and applies --report-dir.
DevProxy.Tests/​ReportsFolderTests.cs	Tests config and CLI path resolution.
DevProxy.Tests/​Fakes.cs	Adds the report-folder property to the test fake.
DevProxy.Plugins/​Reporters/​PlainTextReporter.cs	Passes proxy configuration to the base reporter.
DevProxy.Plugins/​Reporters/​MarkdownReporter.cs	Passes proxy configuration to the base reporter.
DevProxy.Plugins/​Reporters/​JsonReporter.cs	Passes proxy configuration to the base reporter.
DevProxy.Plugins/​Reporters/​BaseReporter.cs	Creates and uses the output folder; retains the original constructor.
DevProxy.Integration.Tests/​TestProxyConfiguration.cs	Adds report-folder support to integration test configuration.
DevProxy.Integration.Tests/​ReporterReportsFolderTests.cs	Tests folder creation, timestamp suffixes, and working-directory fallback.
DevProxy.Integration.Tests/​JsonReporterTests.cs	Updates reporter construction to supply configuration.
DevProxy.Abstractions/​Proxy/​IProxyConfiguration.cs	Exposes the report output folder in the configuration contract.

_{Review effort: Balanced}