diff --git a/docs/api-conventions.md b/docs/api-conventions.md
index 33c68a2d8..2a89fe5b0 100644
--- a/docs/api-conventions.md
+++ b/docs/api-conventions.md
@@ -121,6 +121,31 @@ gets this wrong. The SPA works around it with a manual override type; see `web/s
 `PlayoutAlternateSchedule`, `PlayoutTemplate`, and their request types). Copy this pattern for any
 new DTO with a `DayOfWeek` (or `DayOfWeek[]`) member — don't trust the generated numeric type.
 
+### 5a. Runtime JSON casing vs the generated spec (the `ffmpegProfileId` wart)
+
+Runtime `/api/*` JSON is serialized by **Newtonsoft** (`AddNewtonsoftJson` in `Startup.cs`), using
+`ErsatzTV/Serialization/CustomContractResolver.cs` → `CustomNamingStrategy` (camelCase **plus** a
+special case mapping any `FFmpegProfileId` member to `"ffmpegProfileId"`, and honoring any
+`[JsonProperty("...")]` attribute, e.g. `ChannelResponseModel.FFmpegProfile` →
+`[JsonProperty("ffmpegProfile")]`). The OpenAPI document, however, is generated from
+**System.Text.Json** metadata, whose camelCase can differ (it emitted `fFmpegProfileId` /
+`fFmpegProfile`). That drift silently gave the SPA the wrong key to read (issue #198).
+
+Fix (do not remove): `ErsatzTV/Serialization/NewtonsoftSchemaNamingTransformer.cs` is an OpenAPI
+**schema transformer** registered on all three documents (`options.AddSchemaTransformer(...)` in
+`Startup.cs`). For each object schema it resolves the CLR type's Newtonsoft `JsonObjectContract`
+through the *same* `CustomContractResolver` the runtime uses and renames `schema.Properties` (and
+`schema.Required`) keys to the exact names Newtonsoft would emit. This mirrors the wire format **by
+construction**, so future naming-strategy special cases or `[JsonProperty]` renames can't drift.
+
+Guard: `ErsatzTV.Tests/Controllers/OpenApiSerializerContractTests.cs` serializes fully-populated
+DTOs (ChannelViewModel, FFmpegSettingsResponseModel, WatermarkViewModel,
+MediaItemInfoResponseModel) through the runtime Newtonsoft settings and asserts the emitted top-level
+keys equal the corresponding `v1.json` schema's property set. It fails if spec generation ever drifts
+from the MVC serializer again. Note: only exact-match `FFmpegProfileId` gets the special case —
+`DefaultFFmpegProfileId` stays `defaultFFmpegProfileId` under both serializers, and non-acronym or
+single-leading-cap names (`fFmpegPath`, `fFprobePath`, `zIndex`, `rFrameRate`) already agree.
+
 ## 6. Tests
 
 - **Controller tests**: `ErsatzTV.Tests/Controllers/<Domain>ControllerTests.cs`. NUnit + Shouldly +
diff --git a/docs/decisions.md b/docs/decisions.md
index cb237a70f..2242b9ccc 100644
--- a/docs/decisions.md
+++ b/docs/decisions.md
@@ -127,3 +127,19 @@ Sample** (alongside Download Results) while a troubleshooting session is startin
 only gated Download Results. Both downloads compete with the live transcode for I/O and the sample
 archiver reads the same media file, so gating both during a session is strictly safer and costs
 nothing (sessions are short).
+
+## 2026-07-09 — OpenAPI spec mirrors the runtime Newtonsoft serializer (#198)
+
+The generated OpenAPI document is made to follow the **runtime** JSON contract, not the reverse. Runtime
+`/api/*` responses are serialized by Newtonsoft via `CustomContractResolver`/`CustomNamingStrategy`
+(camelCase + a `FFmpegProfileId`→`ffmpegProfileId` special case + `[JsonProperty]` overrides such as
+`ChannelResponseModel.FFmpegProfile`→`ffmpegProfile`), while `Microsoft.AspNetCore.OpenApi` generates the
+spec from System.Text.Json metadata, whose camelCase drifted (`fFmpegProfileId`, `fFmpegProfile`). That
+drift fed the SPA the wrong key. Rather than hand-patch the spec or change the wire format (breaking clients),
+we added `NewtonsoftSchemaNamingTransformer` — an OpenAPI schema transformer registered on all three
+documents that renames each schema property through the *same* Newtonsoft contract resolver the runtime uses,
+so the spec matches the wire format by construction. A contract test
+(`OpenApiSerializerContractTests`) serializes representative DTOs through the real runtime settings and pins
+the spec property sets to them. Decision: **the wire format is the source of truth; the spec follows it via the
+real contract resolver.** This also fixed a latent SPA bug (the channel-list "FFmpeg profile" column read
+`fFmpegProfile` and always showed "Unassigned"). Issue #198.
diff --git a/docs/spa-conventions.md b/docs/spa-conventions.md
index 426f53fa7..ffe2d810b 100644
--- a/docs/spa-conventions.md
+++ b/docs/spa-conventions.md
@@ -76,6 +76,15 @@ One file per domain in `web/src/api/`, e.g. `logs.ts`, `blocks.ts`, `playouts.ts
 - `web/src/api/index.ts` re-exports everything so screens import from `'../api'`, not from the
   individual domain file directly.
 
+**Trust the generated key casing — it mirrors the runtime.** Since #198 the OpenAPI spec is generated
+to match the runtime Newtonsoft serializer exactly (a schema transformer runs the same contract
+resolver; see `api-conventions.md` §5a), so the generated types carry the real wire keys — including
+Newtonsoft's acronym quirks like `ffmpegProfileId` (channel FFmpeg-profile id) and `ffmpegProfile`
+(channel FFmpeg-profile display name). **Do not** hand-cast responses to "fix" a key or dual-read a
+spec-cased vs runtime-cased key (the old `PlaybackTroubleshootingScreen` `#198` escape hatch that read
+`data.channel.fFmpegProfileId` has been removed — read `ffmpegProfileId` straight off the typed
+response). When you mock an API response in a test, use the generated (runtime) casing.
+
 ## 5. Artwork rendering
 
 Render `item.artwork` / `item.poster` (or whatever the DTO field is named) **directly as an `<img