Migrate internal architecture docs to docs/internal

docs/internal/validators.md

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+# Audita Validators
+
+## Scope
+
+This document describes validator composition, execution order, and decision handling.
+
+## Ownership
+
+Built-in validator keys and chains:
+- `internal/validators`
+
+Shared validator runtime mechanics:
+- `internal/framework/validators`
+
+Execution-class metadata:
+- `internal/validators/metadata`
+
+## Built-In Validator Keys
+
+Deterministic:
+- `proposal_shape`
+- `confidence_threshold`
+- `original_text_presence`
+- `non_empty_corrected_text`
+- `no_effect`
+- `protected_terms`
+
+LLM-backed:
+- `spoken_form_plausibility`
+- `meaning_reversal_review`
+- `editorial_review`
+
+## Built-In Chains
+
+Module chains are defined in `internal/validators/chains.go`.
+Glossary, homophones, spoken_word, and grammar each resolve a fixed ordered chain.
+
+## Runtime Execution
+
+For each module section:
+1. run deterministic validators;
+2. run LLM-backed validators;
+3. record decisions and warnings;
+4. carry only approved proposals forward.
+
+Decision cardinality is enforced: each candidate proposal must receive exactly one decision per validator.
+
+## LLM Validator Batching
+
+LLM validators:
+- build canonical validation request payloads;
+- batch by `validation_max_prompt_tokens`;
+- call structured LLM client using response schema registry.
+
+Oversized single proposals are rejected with `validator_input_too_large`.
+Malformed LLM validator responses are downgraded to warnings and rejected batch decisions.
+
+## Decision and Rejection Reporting
+
+Runner records:
+- `validator_decisions`
+- `validator_rejected`
+- warning records (including malformed response warnings)
+
+Correction ledger classifies deterministic vs LLM validator decisions using canonical metadata classes.
+
+## Key Tests
+
+- `internal/validators/*_test.go`
+- `internal/framework/validators/*_test.go`
+- `internal/framework/processreport/correction_ledger_test.go`
+- `internal/cli/run_test.go`