pad/internal/server/relation_referents.go

package server

import (
	"log/slog"
	"net/http"
	"sort"
	"strings"

	"github.com/PerpetualSoftware/pad/internal/items"
	"github.com/PerpetualSoftware/pad/internal/models"
	"github.com/PerpetualSoftware/pad/internal/store"
)

// Server-side half of referent validation for `relation` values (PLAN-2857 U1
// / TASK-2878). The store owns the question "does this value name a live item
// in the declared target collection"; this file adds the one part that is
// request-scoped — whether the caller may SEE that item — and turns the result
// into whatever each door owes its caller.
//
// Eight doors reach `items.CoerceFields`, and they do NOT all owe the same
// thing, which is why this is a value-returning helper rather than a
// write-the-response one in the `extractParentLink` mould:
//
//   - The six WRITE doors (create, update-fields, update-fields_patch,
//     same-workspace move, bulk update, bulk move) refuse: a caller who
//     supplied a value asserted it, and an unresolvable assertion is a 400.
//   - The two COPY doors report instead. A relation value CARRIED from a
//     source item points at a source-workspace row and cannot resolve in the
//     destination by construction; that is an unportable referent, not a bad
//     write, and the copy already drops such things (`github_pr`, reason
//     `referent_not_portable`). Refusing would make every copy of a related
//     item start failing and would reintroduce the cross-workspace relation
//     case PLAN-2857 excludes from v1. An override SUPPLIED to a copy is a
//     write like any other and still refuses.

// resolveRelationReferents runs the store resolver and then drops any target
// the requester cannot see, reporting it as `not_found`.
//
// Visibility is folded into the SAME issue vocabulary rather than given its
// own reason on purpose: telling a caller "that item exists but you may not
// see it" is an existence oracle, which this codebase has a standing rule
// against. The store's `not_found` and a visibility failure must be
// indistinguishable on the wire.
func (s *Server) resolveRelationReferents(
	r *http.Request,
	workspaceID string,
	schema models.CollectionSchema,
	fieldMap map[string]any,
) ([]store.RelationIssue, error) {
	return s.resolveRelationReferentsAs(r, workspaceID, workspaceRole(r), schema, fieldMap)
}

// resolveRelationReferentsAs is resolveRelationReferents with the requester's
// effective role passed EXPLICITLY rather than read from the request.
//
// The cross-workspace copy and its preflight need this. `workspaceRole(r)` is
// the role the middleware stashed for the workspace in the URL — the SOURCE —
// and a relation override on a copy names an item in the DESTINATION, where
// the caller's role can be different or absent. `CrossWorkspaceAccess.Role`
// is that role, derived fresh from membership and grants, and its own doc says
// in as many words never to substitute `workspaceRole(r)` for it.
func (s *Server) resolveRelationReferentsAs(
	r *http.Request,
	workspaceID string,
	role string,
	schema models.CollectionSchema,
	fieldMap map[string]any,
) ([]store.RelationIssue, error) {
	return s.resolveRelationReferentsAsQ(s.store.Q(), r, workspaceID, role, schema, fieldMap)
}

// resolveRelationReferentsAsQ is resolveRelationReferentsAs with every read on
// q: the app installer re-runs it on the provisioning transaction (TASK-3397).
func (s *Server) resolveRelationReferentsAsQ(
	q store.Queryer,
	r *http.Request,
	workspaceID string,
	role string,
	schema models.CollectionSchema,
	fieldMap map[string]any,
) ([]store.RelationIssue, error) {
	// The ORIGINAL values, captured before the store resolver rewrites a ref
	// into its target's UUID. Every issue this function raises quotes what the
	// CALLER sent, never the canonical form: a refusal for an item the
	// requester may not see must not hand back that item's UUID, which would
	// confirm both its existence and its canonical identity — the existence
	// oracle the `not_found` collapse exists to prevent, reopened by the
	// message (codex round 2).
	supplied := make(map[string]string, len(fieldMap))
	for k, v := range fieldMap {
		if str, isStr := v.(string); isStr {
			supplied[k] = str
		}
	}
	quoted := func(key, canonical string) string {
		if orig, ok := supplied[key]; ok && orig != "" {
			return orig
		}
		return canonical
	}

	issues, err := s.store.ResolveRelationReferentsQ(q, workspaceID, schema, fieldMap, s.relationVisibility(r, role))
	if err != nil {
		return nil, err
	}

	// Everything the store resolved is now a canonical ID in fieldMap. Check
	// each one against the requester before it is allowed to stand.
	for _, def := range schema.Fields {
		if !def.IsRelation() {
			continue
		}
		raw, exists := fieldMap[def.Key]
		if !exists || raw == nil {
			continue
		}
		if def.IsMultiRelation() {
			// PLAN-2857 U4, lead ruling day 64: a `multi_relation` element's
			// visibility is judged in the SHARED per-element resolver
			// (`resolveRelationValueQ`), which now consults `canSee` on the
			// UUID and REF rungs for BOTH types — one site, so the two shapes
			// cannot drift. This pass's scalar arm stays as a second read that
			// also catches a target deleted between the resolver's lookup and
			// now; there is nothing left for it to add per element, and an
			// array has no single `id` for it to re-read.
			continue
		}
		id, isStr := raw.(string)
		// TRIMMED, matching the store resolver: it ignores a whitespace-only
		// value as "no reference", so an untrimmed check here refuses a value
		// the store never objected to — and since the vanished-target arm
		// below turns a missing lookup into a refusal, `"   "` became a
		// not_found instead of an empty field (codex round 6).
		if !isStr || strings.TrimSpace(id) == "" {
			continue
		}
		if ri, already := issueForKey(issues, def.Key); already {
			// `wrong_collection` is the one issue that names a LIVE item, so
			// its message ("is not an item in collection X") tells the caller
			// the value EXISTS — distinguishable from the `not_found` a
			// nonexistent value gets, and therefore an existence oracle for
			// anyone who cannot see that item (codex round 3). Collapse it to
			// `not_found` when the requester may not see the target; keep the
			// specific message when they may, because "you linked a task
			// where a person belongs" is the useful half of this reason.
			//
			// Any other issue is already `not_found`-shaped and needs nothing.
			// An `ambiguous` reason arrives already decided: since the
			// resolver takes this requester's visibility predicate, its count
			// is the VISIBLE count and there is nothing left to narrow here.
			// It used to be re-decided in this layer, which left the copy
			// transaction — where no server pass runs — leaking.
			if ri.Reason != store.RelationTargetWrongCollection {
				continue
			}
			if !ri.VisibilityChecked {
				// See failClosedUnjudged (BUG-3012).
				failClosedUnjudged(issues, def.Key, "main")
			}
			continue
		}
		item, err := s.store.GetItemQ(q, id)
		if err != nil {
			return nil, err
		}
		if item == nil {
			// It resolved moments ago and is gone now — soft-deleted between
			// the two reads. Treated as unresolvable rather than waved
			// through: this whole unit exists to stop a dangling referent
			// reaching the blob, and "the target vanished mid-request" is the
			// one case where letting it through would be a deliberate one.
			// Same `not_found` the resolver would have given a moment later,
			// so a retry reports it identically.
			issues = append(issues, store.RelationIssue{
				Key: def.Key, Value: quoted(def.Key, id), Target: def.Collection,
				Reason: store.RelationTargetNotFound,
			})
			continue
		}
		visible, err := s.checkItemVisibleQ(q, workspaceID, item, currentUser(r), role, isBearerAuth(r))
		if err != nil {
			return nil, err
		}
		if !visible {
			issues = append(issues, store.RelationIssue{
				Key: def.Key, Value: quoted(def.Key, id), Target: def.Collection,
				Reason: store.RelationTargetNotFound,
			})
		}
	}
	return issues, nil
}

// issueForKey returns the issue already raised for key, if any.
func issueForKey(issues []store.RelationIssue, key string) (store.RelationIssue, bool) {
	for _, ri := range issues {
		if ri.Key == key {
			return ri, true
		}
	}
	return store.RelationIssue{}, false
}

// collapseIssue rewrites the reason of the issue already raised for key. In
// place, because the slice is what the caller renders.
func collapseIssue(issues []store.RelationIssue, key string, reason store.RelationIssueReason) {
	for i := range issues {
		if issues[i].Key == key {
			issues[i].Reason = reason
			return
		}
	}
}

// collapseInvisibleRelationIssues is the LATE pass's guard against an
// unjudged `wrong_collection` reaching a caller: the same rule
// resolveRelationReferentsAs applies to the MAIN pass.
//
// Late-default issues reach a caller: each door feeds them to
// RequiredRelationIssues and renders the result into a 400 or a preflight
// `needs_value` row. `wrong_collection` is the one reason that names a LIVE
// item, so an invisible target announced that way is the existence oracle
// round 3 closed, reopened through the door round 10 added (codex round 15).
// Applied at all five late-default sites, per CONVE-18.
//
// Since the day-64 ruling, `store.ResolveLateRelationDefaults` takes the
// requester's visibility func and judges every rung itself, so its issues
// arrive with VisibilityChecked set and this pass leaves them alone. An issue
// without it fails closed, with no second lookup (failClosedUnjudged,
// BUG-3012).
func (s *Server) collapseInvisibleRelationIssues(r *http.Request, workspaceID, role string, issues []store.RelationIssue) error {
	for i := range issues {
		if issues[i].Reason != store.RelationTargetWrongCollection || issues[i].VisibilityChecked {
			continue
		}
		// See failClosedUnjudged (BUG-3012).
		failClosedUnjudged(issues, issues[i].Key, "late")
	}
	return nil
}

// failClosedUnjudged collapses a `wrong_collection` issue that reached a
// server pass WITHOUT the resolver having judged it against the requester
// (VisibilityChecked false), and does so with NO lookup (BUG-3012).
//
// `wrong_collection` names a live item, so an unjudged one is an existence
// oracle waiting for a caller who cannot see it. Both passes used to settle
// that by RE-RESOLVING the value and checking visibility on what came back,
// which was a second lookup of a value the resolver had already looked up:
// a delete between the two turned a visible caller's specific message into
// `not_found`. Since the day-64 ruling moved visibility into the resolver,
// every server feeder hands it a non-nil relationVisibility, and both sites
// that build this reason stamp VisibilityChecked when they had one. The one
// resolution that deliberately runs WITHOUT one, MigrateRelationReferentsQ's
// carried branch (survival must not depend on the mover), judges its
// wrong_collection REASONS itself against the matched row. So nothing reaches
// here; a server test run counts zero of this log line (BUG-3012 trail).
//
// It stays as a FAIL-CLOSED guard rather than being deleted outright,
// because the store documents a nil visibility func as legitimate ("count
// every live match", for import and migrate): a future feeder that passes
// nil would otherwise hand an unjudged issue straight to a caller. Collapsing
// discloses less, never more, and the log says a feeder skipped the
// resolver's visibility argument.
func failClosedUnjudged(issues []store.RelationIssue, key, pass string) {
	slog.Warn("relation issue reached the server without a visibility judgement; collapsing to not_found",
		"key", key, "pass", pass)
	collapseIssue(issues, key, store.RelationTargetNotFound)
}

// refuseRelationIssues writes the 400 a write door owes and reports whether it
// did. One function so the six refusing doors cannot phrase the same refusal
// three different ways, and so a client matching on the error code sees one
// answer from every door.
//
// The message names the field, the value AS SUPPLIED, and the target
// collection — the three things a caller needs to fix it without a second
// request. Every issue is rendered, joined; a schema has a handful of relation
// fields at most, and reporting one at a time would make fixing a bulk import
// an N-round-trip exercise.
//
// Deliberately the ORDINARY `validation_error` shape, with no new details key.
// Two reasons: the MCP stdio transport classifies errors by matching CLI
// stderr PROSE, so a structured field it cannot see would help nobody there;
// and a new error shape is a contract change for every client, which is not
// what this unit is for.
func refuseRelationIssues(w http.ResponseWriter, issues []store.RelationIssue) bool {
	if len(issues) == 0 {
		return false
	}
	writeError(w, http.StatusBadRequest, "validation_error", relationIssuesMessage(issues))
	return true
}

// relationIssuesMessage is the same rendering for the doors that RETURN an
// error instead of writing a response — `createItemChecked` (*itemCreateError)
// and the two bulk operations (*bulkOpError). Split out rather than duplicated
// so a caller cannot accidentally produce a different sentence for the same
// refusal depending on which door it came through.
//
// DELEGATES to store.RelationIssuesMessage rather than joining here (TASK-2878).
// The eighth door refuses inside `internal/store` — the cross-workspace copy,
// through *FieldValidationError — so the sentence has to be reachable from
// there too. Two joins in two packages is how one refusal acquires two
// phrasings, which is the drift this unit exists to remove.
func relationIssuesMessage(issues []store.RelationIssue) string {
	return store.RelationIssuesMessage(issues)
}

// refuseInvisibleRelationOverrides is the visibility check the MIGRATE doors
// owe their SUPPLIED half.
//
// The four write doors go through resolveRelationReferents, which adds
// checkItemVisible on top of the store resolver. The migrate doors call
// store.MigrateRelationReferents directly — it is a store function and cannot
// answer a request-scoped question — so without this their supplied overrides
// resolved against the database alone. This unit's own rule says a supplied
// value is an ordinary write; an ordinary write cannot name an item the
// requester may not see, and a caller able to edit both collections could
// otherwise point a relation at a hidden one.
//
// Only relation keys are probed, on a COPY of the values: the store call that
// follows does the canonicalising write, and a helper that also mutated would
// leave two functions writing one map.
//
// `role` is explicit for the reason resolveRelationReferentsAs documents — at a
// cross-workspace copy the relevant role is the caller's in the DESTINATION.
func (s *Server) refuseInvisibleRelationOverrides(
	r *http.Request,
	workspaceID string,
	role string,
	schema models.CollectionSchema,
	supplied map[string]any,
) ([]store.RelationIssue, error) {
	if len(supplied) == 0 {
		return nil, nil
	}
	probe := make(map[string]any, len(supplied))
	for _, def := range schema.Fields {
		if !def.IsRelation() {
			continue
		}
		if v, ok := supplied[def.Key]; ok && v != nil {
			probe[def.Key] = v
		}
	}
	if len(probe) == 0 {
		return nil, nil
	}
	return s.resolveRelationReferentsAs(r, workspaceID, role, schema, probe)
}

// notDefaultKeys delegates to store.NotDefaultKeys.
//
// The rule moved into `store` because the cross-workspace COPY needs it from
// inside its transaction, and the lead's day-58 ruling is that both doors run
// ONE classifier rather than two kept in step by hand. Kept as a wrapper so
// the four server call sites read unchanged.
func notDefaultKeys(supplied, carried map[string]any) map[string]bool {
	return store.NotDefaultKeys(supplied, carried)
}

// dropInvisibleRelationDefaults is the visibility check a LATE-RESOLVED
// DEFAULT owes (codex round 11).
//
// `ResolveLateRelationDefaults` lives in `store` and resolves against the
// database alone. At the write doors the caller's own values are filtered out
// of the refusal set before it runs — correctly, since a default is not caller
// input — but that also removed the visibility issues raised against those
// keys, and the store then re-resolved them with no visibility layer at all.
// The write's RESPONSE carries the item's fields, so the caller received the
// canonical id of an item they cannot see.
//
// DROPPED, not refused, because the origin has not changed: the schema author
// chose the value and the caller can neither fix it nor be blamed for it. What
// they must not get is the id.
//
// Reported through the same `not_found` reason every other visibility failure
// collapses to, so a caller cannot tell "the default names something you may
// not see" from "the default names nothing".
//
// `notADefault` is every key that is NOT a destination default — the caller's
// own values and the values carried from a source item. Both are excluded
// deliberately and for different reasons: a caller's value is refused
// elsewhere by the visibility check on its own door, and a CARRIED value must
// never be refused or dropped for visibility at all, because that would make
// an item referencing something the mover cannot see unmovable. The first
// version of this took "present before the late pass", which at a migrate door
// includes the defaults MigrateFields injected — so exactly the values it
// dropInvisibleRelationDefaults removes destination-schema defaults whose
// target this requester cannot see, reporting each as a `not_found` drop.
//
// The body moved to store.DropInvisibleRelationDefaultsQ so the cross-workspace
// COPY — which resolves its late defaults inside its own transaction and could
// not reach a *Server method — runs the SAME code rather than a second
// implementation of the same rule. That door was the one site of five that
// never got this pass, because round 15's sweep enumerated the sites reachable
// from `internal/server` and the class is one wider than the package
// (night-11 finding, lead ruling day 58).
//
// The request-scoped part stays here, as the closure: who is asking, their role
// in this workspace, and whether the call is bearer-authenticated.
func (s *Server) dropInvisibleRelationDefaults(
	r *http.Request,
	workspaceID string,
	role string,
	schema models.CollectionSchema,
	fieldMap map[string]any,
	notADefault map[string]bool,
) ([]store.RelationIssue, error) {
	return s.dropInvisibleRelationDefaultsQ(s.store.Q(), r, workspaceID, role, schema, fieldMap, notADefault)
}

func (s *Server) dropInvisibleRelationDefaultsQ(
	q store.Queryer,
	r *http.Request,
	workspaceID string,
	role string,
	schema models.CollectionSchema,
	fieldMap map[string]any,
	notADefault map[string]bool,
) ([]store.RelationIssue, error) {
	return s.store.DropInvisibleRelationDefaultsQ(q, workspaceID,
		s.relationVisibility(r, role), schema, fieldMap, notADefault)
}

// relationVisibility binds the request-scoped half of the visibility rule into
// a callback the store can run on ITS executor. This is what lets the copy
// apply the rule inside the transaction that holds both workspaces' advisory
// locks — the shape `checkItemVisibleQ` is parameterised for (BUG-2409).
func (s *Server) relationVisibility(r *http.Request, role string) store.RelationVisibilityFunc {
	user := currentUser(r)
	bearer := isBearerAuth(r)
	return func(q store.Queryer, workspaceID string, item *models.Item) (bool, error) {
		return s.checkItemVisibleQ(q, workspaceID, item, user, role, bearer)
	}
}

// resolveRelationsForWrite is the whole relation decision for a WRITE door —
// create and the full-`fields` update, which ran the identical four steps.
//
// Extracted after codex round 10 showed the same rule stated at a third site
// (CONVE-139: consolidate when the move is mechanical, do not defer for
// effort). The rule is: the CALLER's values are refused, and everything
// validation filled in is dropped and reported. Four steps expressed that, and
// two doors each spelled all four out:
//
//  1. resolve the whole map, which is caller input plus injected defaults;
//  2. keep only the issues on keys the caller actually supplied — a default is
//     asserted by nobody, so an unresolvable one must not refuse the write;
//  3. resolve the defaults validation injected AFTER the main pass, dropping
//     what does not resolve — except in a REQUIRED field, where dropping
//     would store the item with that field absent;
//  4. drop a default whose target the caller cannot see, so the response does
//     not hand back its id.
//
// NOT extended to the migrate doors, and not for effort: they reach the same
// rule through `store.MigrateRelationReferents`, which is in `internal/store`
// and cannot call this — the visibility layer here is request-scoped by
// construction, and `store` cannot import `server`. Unifying the two families
// needs a caller-supplied visibility predicate on the store API; that is
// IDEA-2886, with its own door table.
//
// `refusals` are the caller's to fix; `dropped` are keys the write discarded
// and must report.
func (s *Server) resolveRelationsForWrite(
	r *http.Request,
	workspaceID string,
	role string,
	schema models.CollectionSchema,
	fieldMap map[string]any,
	presentBefore map[string]bool,
	posture relationPosture,
) (refusals []store.RelationIssue, dropped []string, err error) {
	return s.resolveRelationsForWriteQ(s.store.Q(), r, workspaceID, role, schema, fieldMap, presentBefore, posture)
}

// resolveRelationsForWriteQ is resolveRelationsForWrite with every read on q
// (TASK-3397: the installer's in-transaction normalization).
func (s *Server) resolveRelationsForWriteQ(
	q store.Queryer,
	r *http.Request,
	workspaceID string,
	role string,
	schema models.CollectionSchema,
	fieldMap map[string]any,
	presentBefore map[string]bool,
	posture relationPosture,
) (refusals []store.RelationIssue, dropped []string, err error) {
	issues, err := s.resolveRelationReferentsAsQ(q, r, workspaceID, workspaceRole(r), schema, fieldMap)
	if err != nil {
		return nil, nil, err
	}
	callerIssues := store.IssuesForCallerInput(issues, presentBefore)
	if len(callerIssues) > 0 && posture == relationsRefuse {
		// The write is about to be REFUSED, so steps 3 and 4 would only
		// prepare a field map nobody stores.
		return callerIssues, nil, nil
	}
	// A CARRYING door does not stop here, and this is the round-15 defect:
	// the early return was written when every caller of this path refused, and
	// stayed when the artifact-import door began carrying instead. An import
	// holding ONE unresolvable caller value would skip the late-default pass
	// AND the default-visibility drop entirely, storing whatever the
	// destination schema injected — including a default the caller cannot see
	// — and reporting none of it. The refusals are still returned; they are
	// the carry report, not a stop.

	lateDropped, err := s.store.ResolveLateRelationDefaultsQ(q, s.relationVisibility(r, role), workspaceID, schema, fieldMap, presentBefore)
	if err != nil {
		return nil, nil, err
	}
	if cerr := s.collapseInvisibleRelationIssues(r, workspaceID, role, lateDropped); cerr != nil {
		return nil, nil, cerr
	}
	if required := store.RequiredRelationIssues(schema, lateDropped); len(required) > 0 {
		return append(callerIssues, required...), nil, nil
	}

	invisible, err := s.dropInvisibleRelationDefaultsQ(q, r, workspaceID, role, schema, fieldMap, presentBefore)
	if err != nil {
		return nil, nil, err
	}
	// The required check covers the INVISIBLE drops too. It was written for
	// `lateDropped` and a sibling list was added beside it a round later —
	// deleting a key after validation has passed leaves a required field
	// absent regardless of which list recorded it (codex round 13).
	if required := store.RequiredRelationIssues(schema, invisible); len(required) > 0 {
		return append(callerIssues, required...), nil, nil
	}
	for _, ri := range append(lateDropped, invisible...) {
		dropped = append(dropped, ri.Key)
	}
	// callerIssues is EMPTY on a refusing door — it returned above — and holds
	// the carry report on a carrying one. Returning it here rather than `nil`
	// is what keeps an import's unresolvable values named in the response now
	// that the carrying door runs to the end.
	return callerIssues, dropped, nil
}

// structuralOverrideError classifies the problems with a caller's field
// overrides that are about the REQUEST rather than about the workspace's
// state, and is the one classifier both copy doors run before any semantic
// check (lead ruling, day 58).
//
// Two kinds, in this order:
//
//	malformed_override — an override names a field the destination schema does
//	                     not declare.
//	invalid_override   — an override's VALUE fails the destination's type for
//	                     that field.
//
// STRUCTURAL BEFORE SEMANTIC, and the preflight's order is the contract. The
// copy used to run refuseInvisibleRelationOverrides — a question about what
// this caller may SEE — before the store call that performs these checks, so
// `{"owner_ref":"<invisible>","ghost":"x"}` returned `malformed_override` from
// the preflight and `validation_error` from the copy, and `{"owner_ref":42}`
// returned `invalid_override` from the preflight and `validation_error` from
// the copy. One body, two answers, which is the DR-6 divergence this pair
// exists to prevent (codex round 19).
//
// One function rather than two orderings kept in step by hand: the previous
// arrangement was not that anyone chose the wrong order, it was that the order
// was an emergent property of where each check happened to live.
//
// Returns ok=true when nothing structural is wrong.
func structuralOverrideError(overrides map[string]any, targetSchema models.CollectionSchema) (code, message string, ok bool) {
	if len(overrides) == 0 {
		return "", "", true
	}
	schema := items.SchemaForMigratedFields(targetSchema)
	if bad := items.UndeclaredOverrideKeys(overrides, schema.Fields); len(bad) > 0 {
		return "malformed_override", "Destination collection has no field(s): " + summarizeKeys(bad), false
	}
	// Validated in ISOLATION — the overrides alone, never merged over the
	// migrated map — so the answer cannot depend on the source item's
	// contents. That is the same property the undeclared check has, and it is
	// what lets this run before anything reads the source.
	probe := make(map[string]any, len(overrides))
	for k, v := range overrides {
		if v == nil {
			// An explicit null is a CLEAR, not a value, and has no type to
			// fail. Validating it here would refuse the documented way to
			// blank a field.
			continue
		}
		probe[k] = v
	}
	if len(probe) == 0 {
		return "", "", true
	}
	// COERCED FIRST, exactly as both doors coerce before validating (BUG-2850).
	// Without this the classifier refuses a value the copy would happily
	// accept — `{"cost":"42"}` against a number field is coercible, and
	// TestCopyAndPreflightCoerceIdentically pins that it must be accepted at
	// both doors. Hoisting a check above the coercion that makes it pass is
	// the same class of error as the ordering this function exists to fix.
	probe = items.CoerceFields(probe, schema)
	var bad []string
	for _, iss := range items.ValidateFieldsDetailed(probe, schema) {
		if iss.Kind != items.IssueInvalid {
			// IssueRequired and friends are about the FINAL map, which this
			// probe is not — a required field the overrides do not mention is
			// not an override problem.
			continue
		}
		if _, overridden := overrides[iss.Key]; !overridden {
			continue
		}
		bad = append(bad, iss.Message)
	}
	if len(bad) > 0 {
		sort.Strings(bad)
		// Bounded for the same reason the malformed_override message is:
		// validateFieldType quotes the offending VALUE verbatim, so a single
		// large override string would otherwise be reflected back in full.
		return "invalid_override", "Invalid override value(s): " + summarizeMessages(bad), false
	}
	return "", "", true
}