Summary

The MEDIA:<path> regex in extract_media() (gateway/platforms/base.py) carries its own hard-coded extension whitelist that has drifted out of sync with SUPPORTED_DOCUMENT_TYPES. Extensions registered as deliverable documents but missing from the regex are silently stripped from response text — no WARNING is logged because the path never reaches validate_media_delivery_path().

This PR aligns the two whitelists and adds a regression test.

Reproduction (before the fix)

from gateway.platforms.base import BasePlatformAdapter

content = "Here is your report:\nMEDIA:/tmp/report.md"
media, cleaned = BasePlatformAdapter.extract_media(content)

# Expected: media == [("/tmp/report.md", False)]
# Actual:   media == []  (path silently stripped, never dispatched)

Same failure mode for .json, .yaml, .toml, .ini, .cfg, .log, .ts, .py, .sh, .xml — all listed in SUPPORTED_DOCUMENT_TYPES (line ~1023) but absent from the regex (line ~2416).

Real-world impact

Surfaced when delivering a .md research report on Telegram. The MEDIA: line vanished from the rendered message; no document attachment; gateway.log showed:

response ready: ... response=404 chars
[Telegram] Sending response (198 chars) to ...

…with no Skipping unsafe MEDIA directive path outside allowed roots warning that normally accompanies allowlist rejection. The 206-char delta corresponds to the three stripped MEDIA: lines.

Fix

Add the missing extensions to the regex alternation:
md | log | json | xml | ya?ml | toml | ini | cfg | ts | py | sh

…and a comment block above the pattern documenting the alignment contract so the next person who edits either side knows to update the other.

Tests

• Parametrized regression (test_media_tag_recognizes_document_extensions) covers every newly-allowed extension.
• Real-world reproduction (test_media_tag_recognizes_markdown_with_quoted_path) — .md path with a leading non-ASCII context line, mirroring the original failure.

Verification

Reverted the gateway/platforms/base.py hunk and re-ran the new tests against the un-fixed code: 13 failures, exactly as expected (12 parametrized + 1 real-world). Restored the fix → 27 passed in TestExtractMedia. Full tests/gateway/test_platform_base.py suite: 114 passed, 2 skipped.

$ pytest tests/gateway/test_platform_base.py
======================== 114 passed, 2 skipped in 0.67s ========================

Scope

Minimal, additive — only adds extensions already enumerated as deliverable per SUPPORTED_DOCUMENT_TYPES. Does not touch extract_local_files() (which already supports these via its own broader list), validate_media_delivery_path(), or the document dispatch path.

A follow-up PR could refactor the regex to construct its alternation from SUPPORTED_DOCUMENT_TYPES programmatically, eliminating the drift class entirely. That's deliberately out of scope here to keep this fix small and reviewable.