… recover

Anthropic enforces two independent per-image ceilings:
  1. 5 MB encoded base64 byte size
  2. 8000px longest side
Pre-fix, every image-oversize guard in Hermes reasoned about
BYTES ONLY. A tall full-page screenshot (e.g. 1200×12000 at
0.06 MB) is well under 5 MB but vastly over 8000px, slipped
through every guard, got baked into immutable conversation
history, and bricked the session on every subsequent replay
with a non-retryable HTTP 400. Recovery required manually
un-pinning the session in sessions.json. See NousResearch#25837 and
NousResearch#37677.

The fix is four coordinated patches, each covering one layer
of the guard chain so any one catches the regression even if
another is bypassed:

1. agent/error_classifier.py — _IMAGE_TOO_LARGE_PATTERNS
   Add the dimension-cap patterns ('image dimensions exceed',
   'dimensions exceed max allowed', 'max allowed size: 8000')
   alongside the existing 5 MB byte patterns. Without this the
   400 falls through to a generic non-retryable bucket and the
   shrink/retry path never fires.

2. tools/vision_tools.py — _MAX_IMAGE_DIMENSION = 7900
   constant + _image_exceeds_dimension() helper. Plus a NEW
   pre-cap pass in _resize_image_for_vision that decodes the
   image dimensions BEFORE the byte-sizing fast-path and
   downscales the longest side to 7900px (100px headroom under
   Anthropic's hard 8000 cap) preserving aspect ratio. The
   pre-cap writes a downscaled tempfile and rebinds image_path
   so the subsequent byte pass operates on the resized version.
   The byte fast-path was previously bailing out on a tiny-but-
   tall image before the resize logic could run; the pre-cap
   fixes that ordering bug.

3. tools/vision_tools.py — embed-time dimension check
   A new proactive check at the vision_analyze_tool / vision
   site, BEFORE the existing embed-time byte cap. Decodes the
   image with PIL (soft dependency, no-ops gracefully when
   Pillow is missing — the reactive recovery in step 4 is the
   safety net), resizes via _resize_image_for_vision when
   either axis exceeds 7900px. This prevents the oversized
   image from ever being baked into history in the first place.

4. agent/conversation_compression.py — reactive shrinker
   Decodes the image dimensions and shrinks on dimension
   violation, not just on byte violation. The old gate was
   'if len(url) <= target_bytes: return None' which silently
   returned False for a 0.07 MB / 1000×11000 tool-result. Now
   the gate is 'if not dim_exceeds and len(url) <= target_bytes:
   return None'. Falls back to byte-only behaviour if Pillow
   is unavailable, so the pre-fix regression cannot recur.

Plus: a new pyproject.toml [project.optional-dependencies] 'vision'
extra pins Pillow==11.1.0. Pillow is the soft dependency that
powers steps 2/3/4; without it the dimension-aware paths
silently no-op. Per the existing 'smaller dependencies =
smaller blast radius' rule, Pillow stays out of core
dependencies and is opt-in via 'pip install
hermes-agent[vision]'.

Tests: tests/tools/test_oversized_image_dimension.py has 11
regression tests covering all four fix sites plus the legacy
byte-pattern guard. Uses real PIL Image.new() / save() to
construct actual 1200×12000 / 1000×11000 fixtures so the
dimension-decode path is exercised end-to-end. The previously
missing assertion that '8000px image is over our 7900 target'
is also pinned to lock the resize target against accidental
drift.

Refs: NousResearch#25837, NousResearch#37677

Seven Copilot inline review comments on NousResearch#37701, all worth landing
in a polish pass before merge:

1. tools/vision_tools.py:432 — temp file leak + Windows handle.
   Switched tempfile.NamedTemporaryFile(...).name (which leaves
   a stale open file handle on Windows) to tempfile.mkstemp +
   explicit os.close(fd) before PIL reopens the path. The
   hard-coded .png suffix is now derived from the actual format
   we save (PNG vs JPEG), so downstream MIME detection that reads
   the file extension doesn't get lied to.

2. tools/vision_tools.py:436 — pre-cap tempfile orphaned on
   Pillow-resize path. Pre-fix, the cleanup only ran on the early
   fast-path return; the Pillow-resize loop returned a candidate
   with the tempfile still on disk, accumulating orphans. Fix uses
   contextlib.ExitStack: register the unlink as a callback when
   the tempfile is created, run the entire function body in a
   try/finally that calls _precap_stack.__exit__() exactly
   once at the end (regardless of which return path was taken).
   Failure paths also pop_all() the stack to avoid double-unlink.

3. agent/conversation_compression.py:688 — decode_error was
   assigned but never used. Now passed to logger.debug() so the
   operator has a breadcrumb when dimension decode fails. Removed
   the variable name from the public docstring contract.

4. agent/conversation_compression.py:694 — same as NousResearch#3 (duplicate
   on a different line of the pre-fix version). Same fix.

5. agent/conversation_compression.py:687 — short-circuit by byte
   condition first, only perform dimension decode when URL is
   within target_bytes (the tiny-but-tall case). Polarity was
   initially inverted in my first polish pass; corrected so the
   decode fires when the byte gate alone would miss the violation
   (the exact case NousResearch#25837/NousResearch#37677 reported).

6. tools/vision_tools.py:336 — grammar: "it brick the session"
   → "it bricks the session". One-character fix.

7. tests/tools/test_oversized_image_dimension.py:32 — unused
   imports Optional and patch. Removed.

All 252 tests on this branch pass (11 vision + 29 reconnect + 47
minimax + 165 api_key_providers; test_platform_reconnect_fd_leak
lives on the separate NousResearch#37679 fd-leak branch).

Diff stat: 3 files changed, 205 insertions, 135 deletions.