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Plausible-value defaults on file-decoded arch/tokenizer/quant: unknown arch exported as Qwen2, APR cache reads an untyped weight as Q4_K (#3850 audit) #4419
Description
Found by the #3850 item-5 audit (aprender-d1, 2026-09-25). The GPU-path Q4_K substitutions it found are fixed on PMAT-3850-resolve-qtype-refuses. These remain. Each one turns an unknown or missing value decoded from a file into a plausible value instead of an error:
crates/aprender-serve/src/apr/cache.rs:200:get_quantized_weight_type(..).unwrap_or(GGML_TYPE_Q4_K). A quantized weight with no type recorded is decoded as Q4_K.crates/aprender-core/src/format/converter/name.rs:10-11:from_model_type(..).unwrap_or(Architecture::Qwen2). An unknown arch gets Qwen2 tensor-name mapping on export (the GPT-2 GGUF export missing hidden_dim metadata (roundtrip fails) #236 shape).crates/aprender-core/src/format/converter/inferred_q4k_config.rs:16,21andwrite_model_config.rs:250:unwrap_or("qwen2")is written permanently into the APRmodel_type, which drives the chat template and rope defaults.crates/aprender-core/src/format/converter/metadata.rs:386andgguf_export_config.rs:312:tokenizer.modeldefaults togpt2, which is wrong for SentencePiece models.crates/aprender-serve/src/tensor_names_fallback.rs:126:_ => "llama". Probably a lookup miss rather than a wrong bind. Verify.
Done when: each one refuses by name or is shown benign by a test. One mutant per site restores the default and goes RED.
Refs #3850
Activity
noahgift commentedon Oct 12, 2026
Branch
w71-e3a/4419-no-plausible-defaults@ d3e2ea8 (4 commits on main 70f8c75; branch only, no PR yet).Each site that read a missing file field as a plausible value now refuses it by name, or derives the value from evidence:
detect_gguf_architecture)general.architecture→ Qwen2qwen35/qwen3moe/qwen2moekeep their table by namea_missing_or_unknown_gguf_architecture_is_refused_not_qwen2REDmodel_typefrom GGUF (save_model_tensors_with_gguf_config_and_tokenizer,write_apr_file_raw)"qwen2"gguf_model_type)a_missing_gguf_architecture_is_refused_not_written_as_qwen2REDtokenizer.ggml.modelon GGUF export (both writers)"gpt2"bpe→gpt2); else merges ⇒gpt2; else key omitted + warningtokenizer_ggml_model_is_recorded_or_evidenced_never_guessedREDrecorded_quant_type)an_unrecorded_quant_type_is_refused_not_q4kREDnormalize_architecture_ => "llama"resolve_globalonly returns a tensor whose name exists in the file and errors with every tried name, so this is a lookup miss, not a wrong bindTwo existing tests pinned the old qwen2 default; one now records an architecture, the other asserts the refusal.
The pre-commit complexity check reads
cache.rstogether with itsinclude!d files. So the two GH-201 streaming loaders incuda_streaming_weights.rs(cognitive 43 and 31, already there before this branch) are split into helpers that behave the same.Receipts (one host, 4 cores, at d3e2ea8 unless noted):
cargo check -p aprender-core -p aprender-serve --lib --tests: rc=0cargo check/clippy -p aprender-serve --lib --features cuda: rc=0 (at 2635a1d, before two test-only commits)cargo test -p aprender-core --lib format::: 4034 passed, 0 failedcargo test -p aprender-serve --lib apr::dequant: 8 passedclippy -D warnings --lib --tests --keep-going: no finding in any changed file. The other 165 findings are already on main, in other aprender-core test code.Not covered here: the GH-181 raw Q4K pass-through (
converter/mod.rs, around :206) maps every GGUF name throughArchitecture::Qwen2.map_name, whatever the file's architecture. It is the same class of default, and I left it out of this branch.noahgift commentedon Oct 14, 2026
Folded into #5311 as a checklist row (TRIAGE-100, 2026-10-14): the open-ticket cap is 100, so this ticket is now tracked on that master and closed as not planned. Nothing is lost: reopen it when its work resumes, and an open PR for it reopens it. Pushed branch:
w71-e3a/4419-no-plausible-defaults.Agent: aprender-clerk
noahgift commentedon Oct 14, 2026
Row moved: #5311 was split into named masters (TRIAGE-100 master naming), so this ticket's checklist row is now on #5328.
Agent: aprender-clerk