What does this PR do?

Problem

BasePlatformAdapter.extract_media() logs spurious File not found warnings
whenever the agent explains the MEDIA: syntax in a response. The regex's
last fallback alternative — a bare \S+ — matches any non-whitespace token,
so plain words, relative tokens, and template placeholders like <filename>
are all captured as media paths. send_document() then fails with
os.path.exists() == False and the gateway emits:

WARNING: File file not found: /home/hermes/outbox/<filename>
WARNING: File file not found: /home/hermes/outbox/file
WARNING: File file not found: /outbox/

Root cause

gateway/platforms/base.py — the named path group in the extract_media
regex ends with |\S+). This makes the fallback match anything:

# Before (too broad)
r'''[`"']?MEDIA:\s*(?P<path>...|(?:~/|/)\S+...extension-list...|\S+)[`"']?'''
#                                                                   ^^^^

Fix

Change the fallback from \S+ to (?:~/|/)\S+ so only strings beginning
with an absolute-path prefix are captured. Relative tokens and plain words no
longer trigger false-positive media sends.

# After (restricted to absolute paths)
r'''[`"']?MEDIA:\s*(?P<path>...|(?:~/|/)\S+...extension-list...|(?:~/|/)\S+)[`"']?'''
#                                                                  ^^^^^^^^^^

Tests

Added test_extract_media_ignores_relative_word_fallback in
tests/gateway/test_signal.py:

• MEDIA:description → empty (plain word, no leading /)
• MEDIA:relative/path.png → empty (relative path, no leading /)
• MEDIA:/tmp/file.ogg → extracted correctly (absolute path still works)

All 3 new assertions pass. Existing test_extract_media_finds_image_tag and
test_extract_media_finds_audio_tag continue to pass.

Visual

flowchart LR
    BUG["❌ Bug: MEDIA:description → captured as media path"] --> WARN["WARNING: File not found"]
    FIX["✅ Fix: MEDIA:description → ignored (no leading /)"] --> OK["No spurious warning"]

Closes #24575

Solution Sketch

• fix the root cause in the touched subsystem instead of layering a broad workaround around the symptom
• keep surrounding behavior stable and avoid unrelated refactors while the area is under review
• prove the change with focused checks on the exact path that regressed

Related Issue

Closes #24575

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

Changes Made

• preserved the existing technical rationale and validation notes inside the template body
• scoped this PR description to the implementation already present on the branch
• aligned the delivery format with .github/PULL_REQUEST_TEMPLATE.md

How to Test

1. Review the existing validation notes preserved in this PR body.
2. Run the focused checks for the touched area.
3. Confirm the scoped change still behaves as described above.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform:

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

Screenshots / Logs

• N/A.