package pipeline

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"

	"textmachine/backend/internal/checks"
	"textmachine/backend/internal/config"
	"textmachine/backend/internal/lang"
	"textmachine/backend/internal/membank"
)

// snapshot.go: materializes snapshotID (§3.2/D5.2/D8) — the content-hash of everything that
// affects the wire bytes OR the resolution of a checkpoint's verdict. Editing any input —
// a loud --resnapshot (= re-paying for the whole book, D15), never a silent false-hit.

// contextSnap freezes the context-assembly knobs (§3.8) inside the snapshot.
// Fixed field order — it is part of a content hash. WS2 dropped STMDepth/OverlapTokens
// (dead carryover knobs — §2а), a structural change folded loudly (§8 manifest).
type contextSnap struct {
	GlossaryInjection   string `json:"glossary_injection"`
	GlossaryTokenBudget int    `json:"glossary_token_budget"`
	CacheTTL            string `json:"cache_ttl"`
}

// segmentationSnap freezes the WS2 output-token chunking budget (draft/edit ceilings + per-pair
// fertility) inside the snapshot, mirroring coverageSnap's discipline: a budget or fertility edit
// re-chunks the book (changes chunk boundaries → the wire), so it is a loud --resnapshot (D30.9),
// never a silent divergence. Unlike coverageSnap it is ALWAYS folded — segmentation always runs and
// its values are wire-determining. Fixed field order — part of a content hash.
type segmentationSnap struct {
	DraftBudgetOut int     `json:"draft_budget_out"`
	EditCeilingOut int     `json:"edit_ceiling_out"`
	FertilityCJK   float64 `json:"fertility_cjk"`
	FertilityOther float64 `json:"fertility_other"`
}

func (r *Runner) segmentationSnapshot() segmentationSnap {
	seg := r.Pipeline.Segmentation
	return segmentationSnap{
		DraftBudgetOut: seg.DraftBudgetOut,
		EditCeilingOut: seg.EditCeilingOut,
		FertilityCJK:   seg.Fertility.CJK,
		FertilityOther: seg.Fertility.Other,
	}
}

// coverageSnap freezes the excision coverage-gate config inside the snapshot, so
// enabling the gate OR tuning its thresholds is a loud --resnapshot, never a silent
// mismatch between an old checkpoint's stored disposition and a changed gate. HONEST
// COST (D15): the snapshotID is folded into every call's RequestHash (render.go), so a
// --resnapshot changes EVERY request_hash → every checkpoint misses → the whole book is
// RE-BILLED, even for byte-identical wire requests whose verdict merely needs
// re-classifying. There is no free "re-classify from the checkpoint" here: the
// content-addressed reuse that COULD make an unchanged wire request free (msgsContentHash,
// render.go) is gated on an UNCHANGED snapshot (stagerun.go), so it never fires across a
// resnapshot. This all-or-nothing re-pay is ACCEPTED for the static acceptance book (the
// gate is loud, divergences do not occur) but is exactly why content-addressed checkpoint
// reuse must be designed before the ongoing/append-chapters mode (D15.2). Only folded when
// ENABLED: tweaking a disabled gate's bounds must not force a re-pin (the gate produces no
// verdicts while off). json.Marshal sorts the LenRatio map keys → deterministic render.
// Mirrors the estimator/max_tokens-policy discipline (render.go) for a NON-wire input that
// still determines a checkpoint's resolved verdict.
type coverageSnap struct {
	Enabled       bool                 `json:"enabled"`
	Version       string               `json:"version,omitempty"`
	LenRatio      map[string][]float64 `json:"len_ratio,omitempty"`
	SentCovMin    float64              `json:"sent_cov_min,omitempty"`
	MinChunkChars int                  `json:"min_chunk_chars,omitempty"`
}

// coverageSnapshot renders the gate's snapshot component: {enabled:false} when off
// (so toggling on is a visible change), the full config + algorithm version when on.
func (r *Runner) coverageSnapshot() coverageSnap {
	cov := coverageSnap{Enabled: r.Pipeline.Gates.Coverage.Enabled}
	if cov.Enabled {
		cov.Version = checks.CoverageGateVersion
		cov.LenRatio = r.Pipeline.Gates.Coverage.LenRatio
		cov.SentCovMin = r.Pipeline.Gates.Coverage.SentCovMin
		cov.MinChunkChars = r.Pipeline.Gates.Coverage.MinChunkChars
	}
	return cov
}

// sanitizerSnap freezes the output-sanitizer gate (D30.3) inside the snapshot, mirroring
// coverageSnap: {enabled:false} when off (so toggling on is a visible --resnapshot), the
// algorithm version when on. It changes a checkpoint's RESOLVED disposition (a defect flips
// the chunk to flagged), never the wire, so a rule edit is a loud re-pin, not a silent
// re-verdict on resume. Folded ONLY when enabled — tweaking a disabled gate must not force a
// re-pin (it produces no verdicts while off). Moves to verdictSnapshotID with D15.2.
type sanitizerSnap struct {
	Enabled bool   `json:"enabled"`
	Version string `json:"version,omitempty"`
}

func (r *Runner) sanitizerSnapshot() sanitizerSnap {
	s := sanitizerSnap{Enabled: r.Pipeline.Gates.Sanitizer.Enabled}
	if s.Enabled {
		s.Version = checks.SanitizerVersion
	}
	return s
}

// banknoteSnap freezes the banknote channel (WS4 §4в, F9) inside the snapshot — the VERDICT-AXIS that
// governs the resolved draft (the slice + the derived-checkpoint), mirroring sanitizerSnap. parser_version
// is the split/parse algorithm version: bumping it re-resolves the stripped draft, so it must be a loud
// --resnapshot even without a prompt edit (§4а point 6). DEVIATION-with-rationale from "mirror
// sanitizerSnap exactly": it is folded via a POINTER with omitempty (nil when the channel is off) rather
// than an unconditional {enabled:false} — so ADDING this optional feature does NOT invalidate every
// banknote-OFF book (incl. the golden fixture), while ENABLING the channel or bumping the parser is still
// a loud snapshot move (the substantive loudness point 6 requires). A snapshot re-pin is never billed for
// a feature a book does not use.
type banknoteSnap struct {
	Enabled bool `json:"enabled"`
	// SliceVersion folds the SLICE algorithm only (banknote.go): it decides where the block is cut, and
	// the cut text is a checkpoint. The PARSE rule rides with the run instead — it produces evidence, not
	// paid bytes, and every run recomputes it from the stored answers.
	SliceVersion string `json:"slice_version,omitempty"`
	// TokenBudget folds bankTokenBudget (FL-1): the extra max_tokens the enabled channel adds to the
	// translator draft (stagerun.go, integration point 5) enters request_hash, but bankSliceVersion
	// versions only the SLICE algorithm — so editing bankMaxLines (or the per-line multiplier)
	// would change the wire without bumping the parser version = a silent re-bill on resume. Folding
	// the resolved budget makes any such edit a loud --resnapshot by mechanism, not discipline.
	TokenBudget int `json:"token_budget,omitempty"`
}

// banknoteSnapshot returns the fold ONLY when the channel is enabled (nil otherwise → omitempty drops it).
func (r *Runner) banknoteSnapshot() *banknoteSnap {
	if !r.Pipeline.Gates.Banknote.Enabled {
		return nil
	}
	return &banknoteSnap{Enabled: true, SliceVersion: bankSliceVersion, TokenBudget: bankTokenBudget}
}

// repairSnap freezes the addressable-defect repair sub-step (pack-16) inside the snapshot. It follows
// banknoteSnap's POINTER discipline rather than coverage/sanitizer's `{"enabled":false}` value form, and for
// the same reason: the field is folded ONLY when the gate is on, so ADDING the feature leaves every existing
// book's payload byte-identical and re-bills nobody. Everything that can change the repaired bytes is here —
// the algorithm version, the model and its resolved wire shape (through the SAME foldModelWire the primary
// and the escalation hop use), the call cap, the class set, and the SHA of every class prompt. The prompts
// need an explicit fold because a repair prompt is not a stage: the per-stage PromptSHA256 fold does not see
// it, and msgsContentHash covers only the host stage's messages, so without this a prompt edit would silently
// reuse checkpoints. BudgetUSD is deliberately NOT folded — a dollar cap is not a wire or verdict input (the
// escalation budget is not folded either), and folding it would re-bill the book on a ceiling edit.
type repairSnap struct {
	Enabled       bool              `json:"enabled"`
	Version       string            `json:"version"`
	Model         string            `json:"model"`
	ModelWire     json.RawMessage   `json:"model_wire,omitempty"`
	MaxCalls      int               `json:"max_calls_per_unit"`
	Classes       []string          `json:"classes"`
	PromptSHA256  map[string]string `json:"prompt_sha256"`
	GuardsVersion string            `json:"guards_version"`
}

// repairSnapshot returns the fold ONLY when the gate is enabled (nil otherwise → omitempty drops it).
func (r *Runner) repairSnapshot() (*repairSnap, error) {
	if !r.Pipeline.Gates.Repair.Enabled {
		return nil, nil
	}
	rep := r.Pipeline.Gates.Repair
	s := &repairSnap{
		Enabled: true, Version: repairVersion, Model: rep.Model,
		MaxCalls: rep.MaxCallsPerUnit, GuardsVersion: repairGuardsVersion,
		Classes: r.repairClasses(), PromptSHA256: map[string]string{},
	}
	for cls, tpl := range r.repairTemplates {
		s.PromptSHA256[string(cls)] = tpl.SHA256
	}
	wire, err := r.foldModelWire(rep.Model)
	if err != nil {
		return nil, err
	}
	s.ModelWire = wire.capability
	return s, nil
}

// memoryVersion is the content-hash of the deterministically materialized injected
// memory (the frozen glossary rows + the normalization/matcher algorithm
// versions), the memory component of the snapshot (D5.2/D8, F1 CLOSED). It is the
// Version() of the bank materialized once before the loop, so a change to the
// glossary — or to the deterministic machinery (trad→simp table, matcher) — fires the
// resnapshot gate LOUDLY instead of a stale checkpoint re-paying a diverged translation.
// nil bank (report path / a book with no glossary) → the empty-materialization hash, a
// stable constant. STM is excluded (rebuilt from checkpoints, §3.2). EVERY row folds
// whatever its status since pack-20 (D39.42 п.3 — an auto/draft row changes the injection
// and hence the re-payment, which the per-chunk content_hash alone never reached);
// the approved-only fold this comment used to describe is gone. See membank.ComputeVersion.
func (r *Runner) memoryVersion() string {
	if r.memory != nil {
		return r.memory.Version()
	}
	return membank.ComputeVersion(nil, r.Pipeline.Gates.Glossary.PostcheckGate)
}

// wave selects which pipeline wave a per-wave snapshot folds (WS1 §1в).
type wave int

const (
	waveDraft wave = iota // DRAFT wave: translator-role stages + the BASE bank version (excl Source:mined)
	waveEdit              // EDIT wave: non-translator stages + the ENRICHED bank version (all approved incl mined)
)

// snapshotID materializes the BOOK-GLOBAL job-context snapshot (§3.2): brief_hash, chunker version,
// context-assembly knobs, the (enriched) memory version and the FULL stage plan. It is the snapshot the
// SEQUENTIAL driver pins every job to; the byte output is unchanged (buildSnapshotID over all stages +
// the enriched memory version reproduces it exactly). Payload is a fixed-field-order content hash.
func (r *Runner) snapshotID() (id, payload string, err error) {
	rep, err := r.repairSnapshot()
	if err != nil {
		return "", "", err
	}
	return r.buildSnapshotID(r.Pipeline.Stages, r.memoryVersion(), rep)
}

// snapshotIDForWave computes the PER-WAVE snapshot (WS1 §1в, ADDITIVE — the wave executor residual pins
// each wave's jobs to it; the sequential driver still uses snapshotID). the draft wave folds the DRAFT stages
// (translator role) + the BASE bank version (Source∈{seed,ruby,auto}, EXCL mined); the edit wave folds the EDIT
// stages (non-translator) + the ENRICHED bank version (all approved incl Source:mined). A the bank-mining stop bank
// enrichment (adding mined rows) moves ONLY the enriched version → ONLY edit-wave snapshot, keeping the draft wave
// checkpoints valid (a single re-pay). Byte-consistent with snapshotID's building — the SAME payload
// struct, only the stage subset and the memory version differ.
func (r *Runner) snapshotIDForWave(w wave) (id, payload string, err error) {
	memVer := r.memoryVersion() // enriched (the edit wave)
	if w == waveDraft {
		memVer = r.baseMemoryVersion()
	}
	// The repair fold rides ONLY the wave that owns the SHIPPING stage — repair runs on the final stage's
	// output, so it can change the resolved bytes of that wave alone. Folding it into both would move the
	// DRAFT-wave snapshot when the gate is flipped, invalidating the paid draft checkpoints and destroying
	// the $0 draft resume the wave split exists to protect (the "re-payment stays ONE" invariant).
	var rep *repairSnap
	if w == r.finalStageWave() {
		var err error
		if rep, err = r.repairSnapshot(); err != nil {
			return "", "", err
		}
	}
	return r.buildSnapshotID(waveStages(r.Pipeline.Stages, w), memVer, rep)
}

// finalStageWave is the wave that owns the SHIPPING (last) stage: the edit wave when the last stage is an editor/other
// role (the normal 2-stage pipeline — the edit unit ships), the draft wave when the pipeline is draft-only (the draft
// itself ships). The wave-aware read-models (export/status) use it to compare a stored final-stage row
// against the correct per-wave snapshot and to know whether the shipping unit is an edit unit or a chunk.
func (r *Runner) finalStageWave() wave {
	n := len(r.Pipeline.Stages)
	if n > 0 && r.Pipeline.Stages[n-1].Role != roleTranslator {
		return waveEdit
	}
	return waveDraft
}

// waveStages partitions the pipeline stages by role for a wave: the draft wave = the translator-role (draft) stages,
// the edit wave = every non-translator (editor/other) stage. Order preserved. The prod C1 core is one draft + one
// edit, so this yields [draft] and [edit] respectively.
func waveStages(stages []config.Stage, w wave) []config.Stage {
	var out []config.Stage
	for _, st := range stages {
		isDraft := st.Role == roleTranslator
		if (w == waveDraft) == isDraft {
			out = append(out, st)
		}
	}
	return out
}

// baseMemoryVersion is the DRAFT-wave (the draft wave) memory component: the BASE bank version (excl Source:mined).
// nil bank → the empty-materialization base hash (a stable constant), mirroring memoryVersion().
func (r *Runner) baseMemoryVersion() string {
	if r.memory != nil {
		return r.memory.BaseVersion()
	}
	return membank.ComputeVersionScoped(nil, r.Pipeline.Gates.Glossary.PostcheckGate, true)
}

// buildSnapshotID materializes the snapshot payload for a given stage subset + memory version (§3.2).
// Extracted from snapshotID so the book-global snapshot (all stages + enriched version) AND the two
// per-wave snapshots (WS1 §1в) share one byte-exact builder — a stage subset / memory version is the
// ONLY axis that differs. Fixed field order (a content hash).
func (r *Runner) buildSnapshotID(stages []config.Stage, memVersion string, repair *repairSnap) (id, payload string, err error) {
	type stageSnap struct {
		Name          string  `json:"name"`
		Role          string  `json:"role"`
		Model         string  `json:"model"`
		PromptVersion string  `json:"prompt_version"`
		PromptSHA256  string  `json:"prompt_sha256"`
		Temperature   float64 `json:"temperature"`
		Reasoning     string  `json:"reasoning"`
		// FewShot folds the stage's few_shot on/off state (D38.4) — but ONLY for a prompt
		// that HAS a ---FEWSHOT--- block (nil/omitted otherwise, so stages without examples
		// keep a byte-identical snapshot). The block IS inside the raw file already folded via
		// PromptSHA256, yet dropping it at render (few_shot:false) leaves PromptSHA256 unchanged
		// while the wire changes, so the resolved flag must be folded to keep a flip a loud
		// --resnapshot rather than a silent false-hit — same discipline as Temperature/Reasoning.
		FewShot *bool `json:"few_shot,omitempty"`
		// ExtraBody of the model changes the request BODY (GLM thinking-off, etc.) —
		// without it a knob edit in models.yaml would silently not invalidate the
		// checkpoints (a review finding). json.Marshal sorts map keys →
		// a deterministic render.
		ModelExtra json.RawMessage `json:"model_extra,omitempty"`
		// Provider-level overrides (local kind overrides the wire
		// temperature/max_tokens AFTER the request-hash is computed) — also affect
		// the actual request; without them a providers.local.max_tokens edit
		// would yield the same snapshot and a false checkpoint-hit on the stand's
		// local path (external-review finding F2).
		ProviderTemp   float64 `json:"provider_temp,omitempty"`
		ProviderMaxTok int     `json:"provider_max_tok,omitempty"`
		// ProviderModel — the local-kind backend tag the provider swaps onto the wire
		// AFTER the request-hash (the actual model that answers). The MOST impactful
		// local override, yet it was missing here while its weaker temp/max_tok siblings
		// were folded: a local swap 8b→14b mid-book keeps the same snapID and resume
		// serves the old model (external-review). Folded so it is a loud --resnapshot.
		ProviderModel string `json:"provider_model,omitempty"`
		// Capability — the model's resolved wire form (D3.1): budget-key,
		// temperature-mode, reasoning-control. Changes the request BODY (max_tokens
		// vs max_completion_tokens, whether to send temperature, the thinking-
		// disabler), so it must enter the snapshot — otherwise a cap edit silently
		// false-hits the checkpoints (the same D5.2 class as the payload below).
		Capability json.RawMessage `json:"capability,omitempty"`
		// EscalateTo + EscalateCapability — the single-hop fallback model and its
		// resolved wire shape (Milestone 2.5). The fallback's request_hash uses ITS model,
		// and its wire body uses ITS capability — both must be in the snapshot, or
		// changing the escalation model / its caps would silently false-hit an
		// escalated chunk's checkpoint (closes the D5.2 escalation-capability techdebt:
		// stages were folded, escalation models were not, until the cycle landed).
		EscalateTo         string          `json:"escalate_to,omitempty"`
		EscalateCapability json.RawMessage `json:"escalate_capability,omitempty"`
		// The fallback model's OTHER wire-affecting inputs, mirroring the primary
		// fold above: its top-level extra_body (merged into the escalation wire body)
		// and its provider-level temperature/max_tokens overrides (local kind). Without
		// these, editing the fallback's extra_body / provider knobs would change the
		// escalation wire but leave the snapshot identical → a silent false-hit on a
		// resumed escalated chunk (self-review: the primary path guards this, escalation
		// did not).
		EscalateExtra          json.RawMessage `json:"escalate_extra,omitempty"`
		EscalateProviderTemp   float64         `json:"escalate_provider_temp,omitempty"`
		EscalateProviderMaxTok int             `json:"escalate_provider_max_tok,omitempty"`
		EscalateProviderModel  string          `json:"escalate_provider_model,omitempty"`
	}
	snap := struct {
		BriefHash        string `json:"brief_hash"`
		ChunkerVersion   string `json:"chunker_version"`
		EstimatorVersion string `json:"estimator_version"`
		// MaxTokensPolicy versions the attempt→max_tokens scaling (Milestone 2): a
		// change to the retry doubling shifts attempt≥1 request_hashes, so it
		// belongs in the snapshot as a loud invalidation (same class as
		// estimator_version, applied to the regeneration axis).
		MaxTokensPolicy string `json:"max_tokens_policy"`
		// ClassifierVersion versions the intrinsic classify() verdict logic (thresholds
		// + order), so a re-verdict on a resumed checkpoint is a loud --resnapshot, not
		// a silent flagged↔ok divergence (external-review; symmetric to coverage).
		ClassifierVersion string `json:"classifier_version"`
		PipelineCore      string `json:"pipeline_core"`
		// Defaults affect maxTokens, and that enters the request-hash: without them
		// a max_output_ratio edit would silently invalidate all checkpoints,
		// bypassing the snapshot gate (a review finding).
		MaxOutputRatio float64 `json:"max_output_ratio"`
		MinMaxTokens   int     `json:"min_max_tokens"`
		// ContextAssembly — the context-assembly knobs (glossary/STM/overlap/TTL,
		// §3.8). Editing them changes the model INPUT once memory enters msgs; we
		// fold BEFORE injection, so an injection-budget change does not miss the
		// resnapshot gate (D5.2). Fixed field order — this is a content hash.
		ContextAssembly contextSnap `json:"context_assembly"`
		// Segmentation — the WS2 output-token chunk/edit-unit budget + fertility (segmentationSnap).
		// It changes chunk boundaries → the wire, so a budget/fertility edit is a loud --resnapshot.
		Segmentation segmentationSnap `json:"segmentation"`
		// RenderFormatVersion versions the FORMAT of the role-injection renderers not captured by
		// memoryMatchVersion (a scope/matcher-algorithm version): the editor constraint block's
		// src→dst layout (WS2 §2в) and the gender-constraint render (WS5). A format change shifts the
		// injected bytes → the wire, so folding it separately keeps a flip a loud --resnapshot.
		RenderFormatVersion string `json:"render_format_version"`
		// LangpackVersion — the loaded language-data pack's content hash (internal/lang, D39.15/16),
		// folded ONLY when a pack is present (omitempty otherwise, so a no-pack book is byte-stable and
		// never re-billed for a feature it does not use). The pack feeds the the bank-mining stop bank-miner; a pack DATA
		// edit changes what it proposes, so folding its version makes a pack edit a loud --resnapshot,
		// drift-proof by mechanism (the pack's bytes ARE its version). Wire-neutral for existing
		// checkpoints (the miner produces Source:mined proposals, inert until owner-approved), but folded
		// per the R1 directive so the run's snapshot durably records which pack version produced it.
		LangpackVersion string `json:"langpack_version,omitempty"`
		// EmbeddedVersion — the content hash of the engine's EMBEDDED language data (internal/lang/data/*:
		// CJK section numerals/terminators feeding chunk boundaries, the Russian glossary/editor injection
		// wire-text, the target-ru sanitizer/checker verdict data). Unlike LangpackVersion it is ALWAYS present
		// (embedded in the binary and used by EVERY book — even a no-pack book still splits 第X章 chapters,
		// injects a Russian block and runs the target checkers), so it folds UNCONDITIONALLY. Its bytes ride
		// the wire (injection.txt) and resolve verdicts (target-ru.txt), yet the plane sat in NO content hash
		// (D39.60 §6.1) — folding it makes an embed-data edit a loud --resnapshot instead of a silent verdict
		// or wire change, drift-proof by mechanism (lang.EmbeddedVersion IS the bytes, like Pack.Version()).
		EmbeddedVersion string `json:"embedded_version"`
		// MemoryVersion — the content-hash of the deterministically materialized injected
		// memory (approved-glossary+summary+series-bible). Not a bump-counter (D8): you
		// cannot forget to recompute it, whereas a forgotten bump would reopen the silent
		// re-payment class D5.2. Until the memory-bank migration (v2) the materialization is
		// empty — the hash is stable; once memory enters msgs, the field changes and the
		// resnapshot gate fires loudly. STM is NOT included here (rebuilt from checkpoints).
		MemoryVersion string `json:"memory_version"`
		// PostcheckGate — the memory-bank post-check gate (E1). When true a post-check
		// miss flips the chunk to flagged; folding its on/off state makes toggling it a
		// loud --resnapshot (it changes a checkpoint's RESOLVED disposition), not a silent
		// re-verdict on resume (same class as coverage/classifier). The post-check
		// ALGORITHM version is already inside MemoryVersion (memoryMatchVersion).
		PostcheckGate bool `json:"postcheck_gate"`
		// Coverage — excision QA-gate config (D12 Q3). It does not touch the wire,
		// but it determines a checkpoint's RESOLVED verdict, so a gate change must be
		// a loud --resnapshot, not a silent re-verdict on resume (coverageSnapshot).
		Coverage coverageSnap `json:"coverage"`
		// StyleCheckVersion versions the cheap deterministic post-check rules (dialogue-dash,
		// yofikator, translit-interjection blocklist, 万/億 magnitude gate — cheapgates.go). They
		// are observability, not wire, but editing a rule shifts the recorded style-flag counts, so
		// a bump is a loud --resnapshot (same verdict class as ClassifierVersion). The ё-policy is
		// part of BriefHash (a book field), so a policy change already re-pins via brief_hash.
		StyleCheckVersion string `json:"style_check_version"`
		// Sanitizer — the output-sanitizer gate (D30.3). Like Coverage it does not touch the wire
		// but determines a checkpoint's RESOLVED verdict (a defect flips the chunk to flagged), so a
		// gate flip / rule edit is a loud --resnapshot. Folded only when enabled (sanitizerSnapshot).
		Sanitizer sanitizerSnap `json:"sanitizer"`
		// Banknote — the banknote channel (WS4). Verdict-axis (governs the sliced/derived draft), folded
		// only when ENABLED (nil→omitempty otherwise), so adding the feature never re-bills an off book.
		Banknote *banknoteSnap `json:"banknote,omitempty"`
		// Repair — the addressable-defect repair sub-step (pack-16). Verdict-axis (it re-points final_hash at
		// a derived checkpoint holding the repaired text), folded only when ENABLED and only into the wave
		// that owns the shipping stage.
		Repair *repairSnap `json:"repair,omitempty"`
		Stages []stageSnap `json:"stages"`
	}{
		BriefHash:         r.Book.BriefHash(),
		ChunkerVersion:    chunkerVersion,
		EstimatorVersion:  estimatorVersion,
		MaxTokensPolicy:   maxTokensPolicyVersion,
		ClassifierVersion: classifierVersion,
		PipelineCore:      r.Pipeline.Core,
		MaxOutputRatio:    r.Pipeline.Defaults.MaxOutputRatio,
		MinMaxTokens:      r.Pipeline.Defaults.MinMaxTokens,
		ContextAssembly: contextSnap{
			GlossaryInjection:   r.Pipeline.Context.GlossaryInjection,
			GlossaryTokenBudget: r.Pipeline.Context.GlossaryTokenBudget,
			CacheTTL:            r.Pipeline.Context.CacheTTL,
		},
		Segmentation:        r.segmentationSnapshot(),
		RenderFormatVersion: membank.RenderFormatVersion,
		LangpackVersion:     r.packVersion(),
		EmbeddedVersion:     lang.EmbeddedVersion(),
		MemoryVersion:       memVersion,
		PostcheckGate:       r.Pipeline.Gates.Glossary.PostcheckGate,
		Coverage:            r.coverageSnapshot(),
		StyleCheckVersion:   checks.CheapGateVersion,
		Sanitizer:           r.sanitizerSnapshot(),
		Banknote:            r.banknoteSnapshot(),
		Repair:              repair,
	}
	for _, st := range stages {
		ss := stageSnap{
			// Model is the RESOLVED model — the one this stage will actually call (label routing applied).
			// That is the ASSIGNED snapshot layer for content labels (D39.26 point 1, discharging D20.2-Q3):
			// the label set itself enters no hash, and its whole wire effect rides here, per stage and per
			// wave — so a label that re-routes only the editor moves only the edit-wave snapshot and the paid
			// draft still resumes at $0. With no labels this is st.Model, byte for byte.
			Name: st.Name, Role: st.Role, Model: st.ResolvedModel,
			PromptVersion: st.PromptVersion, PromptSHA256: r.templates[st.Name].SHA256,
			Temperature: st.Temperature, Reasoning: st.Reasoning,
		}
		// Fold few_shot only where the prompt actually carries a ---FEWSHOT--- block, so
		// stages without examples stay byte-identical in the snapshot (D38.4).
		if r.templates[st.Name].FewShot != "" {
			on := fewShotEnabled(st)
			ss.FewShot = &on
		}
		// Fold the PRIMARY model's wire-affecting inputs (prov-triple, extra_body, resolved capability)
		// via the shared foldModelWire (D39 layer 7, L8-snapshot-fold-copypaste-tripwire): the same
		// helper folds the escalate_to fallback below, so a third model axis (channel B / annotator)
		// reuses it and cannot silently drift the snapshot.
		primary, perr := r.foldModelWire(st.ResolvedModel)
		if perr != nil {
			return "", "", perr
		}
		ss.ProviderTemp, ss.ProviderMaxTok, ss.ProviderModel = primary.provTemp, primary.provMaxTok, primary.provModel
		ss.ModelExtra = primary.extra
		ss.Capability = primary.capability
		// Fold the single-hop fallback model + its wire inputs (Milestone 2.5): both are wire-affecting
		// inputs of an escalated call, so changing them is a loud --resnapshot, not a silent false-hit
		// on an escalated checkpoint. Same fold as the primary — no copy-paste to drift.
		// The hop's fold keeps its EXISTING field names, tags, positions and the "only when there is a hop"
		// population rule (D39.26 point 1, sixth byte-identity condition): a labelled run puts the resolved
		// hop in the SAME slots rather than adding a parallel array, so an unlabelled book's payload is
		// unchanged to the byte.
		if st.ResolvedHop != "" {
			ss.EscalateTo = st.ResolvedHop
			esc, eerr := r.foldModelWire(st.ResolvedHop)
			if eerr != nil {
				return "", "", eerr
			}
			ss.EscalateProviderTemp, ss.EscalateProviderMaxTok, ss.EscalateProviderModel = esc.provTemp, esc.provMaxTok, esc.provModel
			ss.EscalateExtra = esc.extra
			ss.EscalateCapability = esc.capability
		}
		snap.Stages = append(snap.Stages, ss)
	}
	data, err := json.Marshal(snap)
	if err != nil {
		return "", "", err
	}
	sum := sha256.Sum256(data)
	return hex.EncodeToString(sum[:]), string(data), nil
}

// modelWireFold is a model's snapshot-folded wire-affecting inputs: its provider-level
// temperature/max_tokens/model overrides (local kind, applied AFTER the request-hash), its top-level
// extra_body, and its RESOLVED capability (budget-key/temperature-mode/reasoning-control). Extracted
// (D39 layer 7, L8-snapshot-fold-copypaste-tripwire) so the primary model, the escalate_to fallback,
// and any future third model axis fold the SAME way — the copy-paste the old tripwire warned about.
type modelWireFold struct {
	provTemp   float64
	provMaxTok int
	provModel  string
	extra      json.RawMessage // nil when the model has no extra_body → omitted (omitempty)
	capability json.RawMessage // always present (ResolveCapability, the same the client sends)
}

// foldModelWire renders one model's wire-fold. ResolveCapability matches exactly what the client
// sends, and json.Marshal sorts map keys (off_extra_body) → deterministic render. Returns an error
// only on a marshal failure (a struct of scalars/known types cannot fail in practice).
func (r *Runner) foldModelWire(model string) (modelWireFold, error) {
	var f modelWireFold
	if prov, ok := r.Models.Providers[r.Models.Models[model].Provider]; ok {
		f.provTemp, f.provMaxTok, f.provModel = prov.Temperature, prov.MaxTokens, prov.Model
	}
	if extra := r.Models.Models[model].ExtraBody; len(extra) > 0 {
		raw, err := json.Marshal(extra)
		if err != nil {
			return f, err
		}
		f.extra = raw
	}
	capRaw, err := json.Marshal(r.Models.ResolveCapability(model))
	if err != nil {
		return f, err
	}
	f.capability = capRaw
	return f, nil
}