[citizenadam]

Linked issue

Approved issue: #817

What changes

embed_texts sends chunk text verbatim as the embeddings input. VLM-backed
embedding deployments — NVIDIA's current nemotron-*embed* models, for
example — parse data:image/<mime>;base64 anywhere in an input string as an
image part and reject the whole request when VLM serving is disabled:

HTTP 400 image inputs require VLM serving to be enabled on this server

Source code legitimately builds such strings (image_url=f"data:image/png;base64,{...}",
screenshot helpers, docstrings naming the format), so one chunk killed its
batch and, with it, the entire semantic build — repeatedly, from chunk 0, every
session.

This change neutralizes the data:image/ prefix to data-uri:image/ in the
OpenAI-compatible request body only:

• the persisted chunk text is unchanged, so search snippets and provenance keep
  the original bytes;
• fastembed and ollama payloads are unchanged, since neither interprets data
  URIs;
• text/plain, application/json, audio/* data URIs and the uppercase form
  are left alone — they already embed successfully against the same deployment,
  so rewriting them would only perturb vectors;
• the helper borrows when the prefix is absent, so the common row costs one
  substring scan and no allocation.

The trigger is a literal, case-sensitive prefix and the backend does not
validate the payload, so a plain str::replace is enough; no regex is needed
on the request path.

embed_texts is the single request builder for both build batches and
interactive query embeds, so both are covered.

How it was checked

• cargo fmt --check: clean.
• Unit tests (image_data_uri_tests, 7 passed / 0 failed): borrowed
  pass-through, source-line template literal, multiple occurrences per row,
  docstring mention without a payload, non-image data URIs untouched, uppercase
  untouched, and a serialized body assertion that no data:image/ survives.
  Run in the debug profile: cargo test -p agent-file-tools --lib image_data_uri_tests.
  cargo test --release cannot build this crate's lib tests at this commit
  because storage_retention::test_volume_uuid_guard is #[cfg(debug_assertions)];
  that is unrelated to this change.
• End-to-end against https://integrate.api.nvidia.com/v1 with
  nvidia/nemotron-3-embed-1b, on a one-file repository containing
  f"data:image/png;base64,{payload.decode('ascii')}", via aft index:
  • stock 0.62.0: kind=semantic status=gap usable=false reason="openai compatible request failed (HTTP 400 Bad Request): {\"message\": \"image inputs require VLM serving to be enabled on this server\" ...}", exit 2;
  • patched: kind=semantic status=success result_count=4, exit 0.
• Real corpus, both roots that triggered the report, same NVIDIA backend, built
  through aft index into the same storage the plugin uses:
  • /mnt/s/ComfyUI: kind=search status=success result_count=1222,
    kind=semantic status=success result_count=20651 (the stock binary failed
    this root at batch 134/326 with the 400);
  • /go/career-ops: kind=search status=success result_count=3455,
    kind=semantic status=success result_count=3850.
    Exit 0, no build-breaker suspensions recorded afterwards.

Notes for review

• No configuration knob: the rewrite is semantically neutral for an embedder and
  applies only to text that no longer matches the data-URI grammar.
• Synapse and Ollama payload builders are untouched; if a future backend is
  known to parse data URIs, the helper is one call away.

---

AI assistance disclosure: this submission was produced with an AI coding agent
(DeepSeek V4.1 Flash driving an autonomous agent session). The agent reproduced
the failure end-to-end, wrote the patch and tests, and ran the verification
commands listed above; a human operator reviewed the diagnosis and directed the
approach. Review the diff with that in mind.

---

Summary by cubic

Fixes semantic embedding failures where VLM-backed deployments (e.g. NVIDIA's nemotron embed) reject chunks containing data:image/ prefixes as image inputs, returning HTTP 400 and breaking the whole build.

• Rewrites data:image/ to data-uri:image/ only in the OpenAI-compatible request body; persisted chunk text, fastembed and ollama payloads, and non-image data URIs stay byte-identical.
• The rewrite borrows when the prefix is absent, so the common row costs one substring scan and no allocation.
• Adds unit tests covering borrowed pass-through, multiple occurrences, docstring mentions, non-image URIs, and serialized request body.

^{Written for commit 4e48adf. Summary will update on new commits.}

[github-actions]

#817 has the design-approved label; this PR can be reviewed.