fix(deepagents): handle dotfile MIME detection

[PetarVukovicFormify]

Summary

Fix MIME detection for text config files whose names do not have normal extensions, including .env.example, .env.local, .gitignore, .dockerignore, .editorconfig, Dockerfile, Makefile, and LICENSE.

Root cause

getMimeType() only checked extname(filePath). For filenames like .env.example, the detected extension is .example, so DeepAgents treated the file as application/octet-stream. When read_file returned that as a generic file content block, Anthropic-compatible model adapters could forward it as a non-PDF document and hit provider validation errors.

Changes

• Check known full basenames before falling back to extension-based MIME detection.
• Treat .env variants and common extensionless config filenames as text/plain.
• Add regression coverage for these filenames.
• Add a patch changeset for deepagents.

Validation

• corepack pnpm --filter deepagents exec vitest run src/backends/utils.test.ts
• corepack pnpm --filter deepagents exec vitest run src/backends/utils.test.ts src/backends/filesystem.test.ts src/backends/local-shell.test.ts
• corepack pnpm --filter @langchain/sandbox-standard-tests build
• corepack pnpm --filter deepagents typecheck
• corepack pnpm format:check
• corepack pnpm --filter deepagents test:unit
• corepack pnpm lint
• corepack pnpm --filter deepagents build

[changeset-bot]

🦋 Changeset detected

Latest commit: ccbfcd2

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
deepagents	Patch
deepagents-acp	Patch
@deepagents/evals	Patch

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commit: ccbfcd2