Bulk-decide a staged import batch via file export/import, CSV and JSON (Phase 1 of #153)

[DutchJaFO]

Background

Phase 1 of a two-phase plan toward #153 ("Declarative conflict-resolution file for recurring
third-party source conflicts"). Today, resolving a staged batch's ambiguous actions means calling
POST /api/v1/import/actions/{id}/decide once per action — fine for one or two conflicts, tedious
for a batch with many. This issue adds a file-based bulk alternative: export a batch's actions,
edit decisions in the file, re-import to apply them all at once. Phase 2 (#153) will generalize the
per-action decisions this issue produces into reusable, persistent per-source rules.

Depends on #162 (Source field decidability), #149, #154 (decide/undo/apply machinery, staging
engine).

Correction (2026-07-24, re-verified before implementation): this issue was filed when only Quote
and Source were decidable. Since then, #171 (StageDirection), #172 (SoundCue), #173 (Person), #175
(Character), and #176 (Conversation) have all shipped their own Modify/decidability paths, and #206
merged Quotinator.Engine into Quotinator.Core. The scope below has grown accordingly by explicit
developer decision — see the amended items and the new items at the end.

Both CSV and JSON are supported — not JSON-only. The row shape is one row per (action, field)
pair, not one row per action:

ActionId,EntityId,EntityType,Field,ExistingValue,IncomingValue,Decision,CustomValue,MarkCompletenessAs
<guid>,<quoteId>,Quote,quoteText,"old text","new text",,,
<guid>,<quoteId>,Quote,character,"","Neo",Replace,,
<guid>,<sourceId>,Source,date,"1994","1994-06",Custom,"1994-06-15",
<guid>,<characterId>,Character,name,"Blocked Row","New Name",Replace,,Complete

• Decision is Keep/Replace/Custom (blank = not yet decided); CustomValue only matters when
  Decision=Custom.
• MarkCompletenessAs is one value per ActionId group (repeated on every row of that group, or
  left blank) — used to resolve a Blocked action (see below).
• List-valued fields (e.g. Quote's genres) use a delimited value in the cell (drama;comedy) — a
  standard CSV convention, no nesting needed.
• This shape is entity-agnostic and serializes identically as JSON (an array of these flat objects).

What needs to be done

1. New GET /api/v1/import/actions/export?batchId=&format=csv|json endpoint (default json) returns
   every decidable field across the batch's actions in the flat shape above. Pending, Decided,
   and Blocked actions are all included — the idea is that bulk-decide is exactly how an operator
   resolves what to do with a Blocked batch, not something scoped out of it. No X-Api-Key
   required, matching GET /import/actions's existing public-read precedent.
2. New POST /api/v1/import/actions/bulk-decide?batchId=&format=csv|json endpoint accepts the edited
   file back, groups rows by ActionId, and applies each action's decision via the existing
   IImportActionService.DecideAsync — reuses existing per-field validation, no new validation logic
   invented. Requires X-Api-Key, matching every other staged-action write endpoint.
3. CSV parsing/writing uses a proper CSV library (quoting, embedded commas/quotes in ExistingValue/
   IncomingValue handled correctly) — not naive string splitting. The existing CsvLineParser
   (Quotinator.Converters.Csv, currently internal) is extracted into a shared, non-internal
   location and reused here, with a matching writer added — no duplicated CSV logic, no new NuGet
   dependency (DRY).
4. Data-domain validation: Decision must be a recognised FieldResolutionChoice member
   (Keep/Replace/Custom); an unrecognised value is a clear per-row error, not silently defaulted.
5. Consumer-domain validation: EntityType must be one of ImportActionEntityTypes.All; Field must
   be a valid, currently-decidable field name for that EntityType. After this issue, every entity
   type is decidable — Series and Universe (the last two without a Modify/decide path) get one as
   part of this issue too (see item 9 below). The reverse (EntityType, Field) → ConflictDecisionRequest
   mapping this requires must cover all nine types explicitly, including Conversation — Conversation's
   description field has no dedicated To*DecisionMap helper today (it's built inline in
   DecideAsync, unlike every other entity's own named helper), so the mapping needs its own explicit
   case for it rather than being derived from a helper that doesn't exist.
6. A row-level error (unknown ActionId, action not part of the requested batchId, invalid
   EntityType, invalid Decision value, unknown Field name, action already applied) reports which
   row failed without aborting the rest of the file — matches POST /import's existing "one bad row
   never aborts the rest" model.
7. GET .../export's output (either format) round-trips through POST .../bulk-decide unmodified
   with zero errors — baseline correctness check before any real edits are made.
8. README.md/addon/DOCS.md endpoint tables updated in the same commit.
9. New: Series/Universe gain Modify/decidability. Both currently match/create purely by Name
   (natural key only, no explicit id, no Correction shape, no Modify path — unlike every other
   entity). They get the same id-present-Correction / id-absent-Creation two-shape treatment Source: explicit file-carried id, decoupling matching from Title/Type/Date content #162
   gave Source and Person: explicit id, Modify/decidability, wire up dateOfBirth/dateOfDeath #173 gave Person: series[]/universe[] schema entries gain an optional id;
   Sql.Series/Sql.Universe gain SelectExistingById/UpdateFieldsById/SelectCompletenessById/
   UpdateCompletenessById; PlanSeriesAsync/PlanUniverseAsync gain an id-match diff flow ahead of
   the existing natural-key path; DecideAsync/ComputeAmbiguousFields/ReverseAppliedActionsAsync/
   ApplyResolvedActionAsync/ClearStaleAddTargetsAsync all gain Series/Universe branches;
   ConflictDecisionRequest gains SeriesName/SeriesUniverseId/UniverseName.
10. New: an already-Decided action's export shows its actual original per-field choice, not a
    guess. Previously, DecideAsync only ever persisted the resolved value (MergedFields) — the
    caller's original Keep/Replace/Custom choice was discarded once the merge ran. This meant
    export could only infer what was chosen (lossy, and ambiguous whenever existing and incoming
    already agreed). System_ImportActions (owned by Quotinator.Data) gains a new additive
    OriginalDecision column; DecideAsync now also writes the caller's actual per-field decision
    there, so a bulk-decide "revise a past decision" is a genuine round-trip, not an approximation.
    This was never a problem before this issue because every previous decide flow was one-shot and
    forward-only (the caller always supplied a fresh decision; the only way to "change your mind" was
    undo, which discards the old decision and starts over) — this is the first feature that needs the
    system to remember and redisplay a prior choice.

Expected tests

Test class	Test method	Starts
Quotinator.Api.Tests	ExportImportActions_Json_ReturnsFlatFieldRows	❌
Quotinator.Api.Tests	ExportImportActions_Csv_ReturnsFlatFieldRows	❌
Quotinator.Core.Tests	DecideAsync_PersistsOriginalDecision_ExportReflectsExactPriorChoice	❌
Quotinator.Api.Tests	BulkDecide_JsonRoundTrip_NoErrors	❌
Quotinator.Api.Tests	BulkDecide_CsvRoundTrip_NoErrors	❌
Quotinator.Api.Tests	BulkDecide_ValidFile_DecidesEveryAction	❌
Quotinator.Api.Tests	BulkDecide_AllNineEntityTypes_DecidesEachCorrectly	❌
Quotinator.Api.Tests	BulkDecide_ConversationRow_DecidesDescriptionViaInlineMapping	❌
Quotinator.Api.Tests	BulkDecide_BlockedAction_ResolvesWithMarkCompletenessAs	❌
Quotinator.Api.Tests	BulkDecide_UnknownActionId_ReportsRowErrorWithoutAbortingOthers	❌
Quotinator.Api.Tests	BulkDecide_InvalidEntityTypeValue_Returns422WithClearMessage	❌
Quotinator.Api.Tests	BulkDecide_InvalidDecisionValue_Returns422WithClearMessage	❌
Quotinator.Api.Tests	BulkDecide_UnknownFieldName_Returns422WithClearMessage	❌
Quotinator.Core.Tests	PlanSeriesAsync_IdMatchFound_FieldsDiffer_StagesModifyAction	❌
Quotinator.Core.Tests	PlanUniverseAsync_IdMatchFound_NameDiffers_StagesModifyAction	❌
Quotinator.Core.Tests	DecideAsync_SeriesModify_ResolvesFieldDecisions	❌
Quotinator.Core.Tests	DecideAsync_UniverseModify_ResolvesFieldDecisions	❌

Definition of done

• All expected tests listed above start red before implementation
• All requirements implemented
• All expected tests pass (green)
• No regression in related tests
• Findings summarised in a closing comment