fix(security): make MCP_UPLOAD_BASE_DIR mandatory for all upload tools

[SavioBS629]

Problem

Directory containment in validateUploadPath was opt-in: the base-dir prefix check only ran if (options.allowedBaseDir), and MCP_UPLOAD_BASE_DIR is unset by default. With it unset, any caller-supplied absolute path to a non-hidden, allow-listed-extension file was accepted, streamed to BrowserStack, and returned as a signed download URL — an arbitrary file read / exfiltration on a default install (GHSA-j4xm-vw5v-c87v).

A previous change added a refuse gate only to the upload-PRD tool (upload-file.ts). The other three upload paths go through the same shared validator and remained exposed:

Tool	File
takeAppScreenshot → uploadApp	appautomate.ts:149
uploadEspressoApp → uploadFileToBrowserStack	appautomate.ts:183
runAppLiveSession → app upload	applive-utils/upload-app.ts:20

Fix

Make containment mandatory in validateUploadPath itself: refuse the upload unless allowedBaseDir is configured, then enforce that the canonicalised path lives inside it. Because all four upload tools share this validator, one change closes the gap uniformly (rather than three separate per-tool gates).

⚠️ Behavior change

App Automate app upload, Espresso app upload, and App Live sessions now require MCP_UPLOAD_BASE_DIR to be set — the same requirement already in place for the upload-PRD tool. Uploads are restricted to that directory. Operators who use these tools must set the env var to a directory containing the files they upload.

Testing

• npm run lint, tsc --noEmit, and vitest run pass. Added validator cases: refuses when no base dir is configured, refuses when the configured base dir doesn't exist, plus the existing containment/extension/hidden-path/size/symlink coverage (updated the two success-path cases to pass a base dir).
• Pre-existing unrelated flakes in buildFailureThemes / tfaRcaCollaboration are present on main and untouched.

🤖 Generated with Claude Code

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[SavioBS629]

Superseded by #420 (same change, branch renamed to drop the internal identifier from the branch name).