feat(files): cache served files and add HTML text viewer

File cache:
- Add my_modules/filecache with metadata, blob, validator and store layers
- Cache convex.get_file via AsyncCache, TTL clamped to the file expiry
- Skip caching for missing, incomplete or already expired records
- Add a process-local, size-bounded LRU for immutable storage blobs
- Build the cache stack from FILE_CACHE_* env vars in build_file_cache
- Attach the cache to the app in my_modules/app/setup.py
- Expose app-bound helpers in filecache/access.py for routes

Serving:
- Send strong ETag, Last-Modified and Cache-Control on served files
- Answer If-None-Match and If-Modified-Since with 304 from metadata only
- Avoid pulling the blob from Convex on a revalidation hit
- Add a short Cloudflare-CDN-Cache-Control edge window for deleted files
- Record cache_status in the wide event on a 304
- Invalidate cached metadata after file update and delete in both routes

Text viewer:
- Add my_modules/textview to render text/plain and text/markdown as HTML
- Linkify http(s) URLs and trim trailing sentence punctuation
- Resolve links pointing at this instance to the referenced file
- Inline image previews, mark missing and expired targets
- Cap resolution at MAX_LOOKUPS backend lookups per document
- Serve the viewer only for real browser navigations, never for curl or CLI
- Keep raw bytes for ?raw=1, downloads and Accept headers without text/html
- Add templates/side/views/webpage/files/text_view.htm with a raw link

Other:
- Add tests for cache layers, serving, text rendering and the route
- Bump multidict to 7.2.1 in uv.lock
- Update the my_helpers submodule pointer

my_modules/textview/__init__.py

@@ -0,0 +1,14 @@
+from .linkify import tokenize
+from .own_links import parse_share_link
+from .render import MAX_LOOKUPS, build_segments
+from .view import build_view_context, decode_text, wants_text_view
+
+__all__ = [
+  'MAX_LOOKUPS',
+  'build_segments',
+  'build_view_context',
+  'decode_text',
+  'parse_share_link',
+  'tokenize',
+  'wants_text_view',
+]

my_modules/textview/linkify.py

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+from __future__ import annotations
+
+import re
+
+# Only http(s) is linkified; everything else stays inert plain text.
+_URL_PATTERN = re.compile(r'https?://[^\s<>"\'`]+', re.IGNORECASE)
+
+# Prose punctuation that is almost never part of the URL itself.
+_TRAILING_PUNCTUATION = '.,;:!?\'"'
+_BRACKET_PAIRS = {')': '(', ']': '[', '}': '{'}
+
+def _trim_trailing(url: str) -> str:
+  """Give punctuation that belongs to the surrounding sentence back to the text."""
+  while url:
+    last = url[-1]
+    if last in _TRAILING_PUNCTUATION:
+      url = url[:-1]
+      continue
+    opening = _BRACKET_PAIRS.get(last)
+    if opening is not None and url.count(opening) < url.count(last):
+      url = url[:-1]
+      continue
+    break
+  return url
+
+def tokenize(text: str) -> list[tuple[str, str]]:
+  """Split text into ('text', value) and ('url', value) tokens, order preserved."""
+  tokens: list[tuple[str, str]] = []
+  cursor = 0
+
+  for match in _URL_PATTERN.finditer(text):
+    url = _trim_trailing(match.group(0))
+    if not url:
+      continue
+
+    start = match.start()
+    end = start + len(url)
+    if start > cursor:
+      tokens.append(('text', text[cursor:start]))
+    tokens.append(('url', url))
+    cursor = end
+
+  if cursor < len(text):
+    tokens.append(('text', text[cursor:]))
+  return tokens

my_modules/textview/own_links.py

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+from __future__ import annotations
+
+from urllib.parse import urlsplit
+
+_ALLOWED_SCHEMES = {'http', 'https'}
+
+def _normalize_host(host: str) -> str:
+  return (host or '').split(',')[0].strip().lower().rstrip('.')
+
+def parse_share_link(url: str, host: str, root_path: str = '') -> str | None:
+  """Return the file_id when url points at this instance's /-<file_id> route."""
+  try:
+    parts = urlsplit(url)
+  except ValueError:
+    return None
+
+  if parts.scheme.lower() not in _ALLOWED_SCHEMES:
+    return None
+  if not parts.netloc or _normalize_host(parts.netloc) != _normalize_host(host):
+    return None
+
+  prefix = (root_path or '').rstrip('/')
+  path = parts.path
+  if prefix:
+    if not path.startswith(prefix + '/'):
+      return None
+    path = path[len(prefix):]
+
+  if not path.startswith('/-'):
+    return None
+
+  file_id = path[2:]
+  if not file_id or '/' in file_id:
+    return None
+  return file_id

my_modules/textview/render.py

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+from __future__ import annotations
+
+from collections.abc import Awaitable, Callable
+
+from .linkify import tokenize
+from .own_links import parse_share_link
+
+# Each resolved link costs one backend lookup, so a single document stays bounded.
+MAX_LOOKUPS = 20
+
+def _media_kind(content_type: str) -> str:
+  value = (content_type or '').split(';')[0].strip().lower()
+  for prefix in ('image', 'video', 'audio'):
+    if value.startswith(prefix + '/'):
+      return prefix
+  if 'pdf' in value:
+    return 'pdf'
+  return 'other'
+
+async def build_segments(
+  text: str,
+  host: str,
+  root_path: str,
+  lookup: Callable[[str], Awaitable[dict | None]] | None = None,
+  max_lookups: int = MAX_LOOKUPS,
+) -> list[dict]:
+  """Turn raw text into template segments: plain text, links and resolved own files."""
+  segments: list[dict] = []
+  resolved: dict[str, dict | None] = {}
+
+  for kind, value in tokenize(text):
+    if kind == 'text':
+      segments.append({'kind': 'text', 'text': value})
+      continue
+
+    file_id = parse_share_link(value, host=host, root_path=root_path) if lookup else None
+    if file_id is None:
+      segments.append({'kind': 'link', 'url': value})
+      continue
+
+    if file_id not in resolved:
+      if len(resolved) >= max_lookups:
+        segments.append({'kind': 'link', 'url': value})
+        continue
+      resolved[file_id] = await lookup(file_id)
+
+    file_data = resolved[file_id]
+    if not file_data:
+      segments.append({'kind': 'link', 'url': value, 'state': 'missing'})
+      continue
+    if file_data.get('expired'):
+      segments.append({
+        'kind': 'link',
+        'url': value,
+        'state': 'expired',
+        'label': file_data.get('file_name') or file_id,
+      })
+      continue
+
+    segments.append({
+      'kind': 'file',
+      'url': value,
+      'state': 'ok',
+      'file_id': file_id,
+      'label': file_data.get('file_name') or file_id,
+      'media': _media_kind(file_data.get('content_type') or ''),
+    })
+
+  return segments

my_modules/textview/view.py

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+from __future__ import annotations
+
+from collections.abc import Awaitable, Callable
+
+from .render import build_segments
+
+# Text types that get the rendered viewer; anything else is served untouched.
+VIEWABLE_CONTENT_TYPES = {'text/plain', 'text/markdown'}
+
+_TRUTHY = {'1', 'true', 'yes'}
+
+def _base_content_type(content_type: str) -> str:
+  return (content_type or '').split(';')[0].strip().lower()
+
+def wants_text_view(content_type: str, accept_header: str, raw_param: str | None, force_download: bool) -> bool:
+  """Only real browser navigations get HTML; curl, wget and the CLI keep the raw bytes."""
+  if force_download or (raw_param or '').lower() in _TRUTHY:
+    return False
+  if _base_content_type(content_type) not in VIEWABLE_CONTENT_TYPES:
+    return False
+  # Accept: */* (curl, wget, CLI clients) must not trigger the viewer.
+  return 'text/html' in (accept_header or '').lower()
+
+def decode_text(raw: bytes) -> str:
+  """Decode the full document; invalid bytes become replacement characters."""
+  return raw.decode('utf-8', errors='replace')
+
+async def build_view_context(
+  raw: bytes,
+  file_name: str,
+  host: str,
+  root_path: str,
+  raw_url: str,
+  lookup: Callable[[str], Awaitable[dict | None]] | None,
+) -> dict:
+  text = decode_text(raw)
+  segments = await build_segments(text, host=host, root_path=root_path, lookup=lookup)
+  return {
+    'file_name': file_name,
+    'segments': segments,
+    'raw_url': raw_url,
+  }