{
  "$schema": "../../schema/run.schema.json",
  "run_id": "next.js--claude-fable-5-1--v6-c--2026-09-28",
  "supersedes": null,
  "replicate_of": null,
  "library": {
    "name": "next.js",
    "ecosystem": "npm",
    "latest_version_at_test": "16.3.6",
    "latest_version_verified_on": "2026-09-28",
    "latest_version_note": "Same verification as `opus-5-5-v6-a` (registry `latest` 16.3.6; graded identifiers re-counted on 16.1.6 / 16.2.0 / 16.3.5 / 16.3.6; executed on the installed 16.3.6: `configSchema` rejects `images.maximumCacheSize` and reports `experimental.clientSegmentCache` as an unrecognised key, the default loader turns `quality: 90` into `q=75`, the bundled OG font is `Geist-Regular.ttf`)."
  },
  "model": {
    "id": "claude-fable-5-1",
    "label": "Claude Fable 5.1",
    "vendor": "Anthropic",
    "invoked_as": "Agent tool, model alias \"fable\"; prompt sent verbatim from prompts/sent/nextjs-v2.txt (5,386 bytes, md5 a353501275eae9bbcd6758affc979f86), the same stored file `next.js/v2` sent on 2026-09-02, pre-registered at 28edbaa before any spawn. Identity probed BEFORE the draw through the same alias in the same session, tool-free: \"I am Claude, model Fable 5.1 (model ID `claude-fable-5-1`), per the system prompt for this session\"; \"My training cutoff is June 2026\". Drawn concurrently with its twin `v6-d` and the Opus 5.5 pair. Pre-registered as the Fable 5.1 charging arm.",
    "self_reported_cutoff": "2026-06",
    "cutoff_basis": "Self-reported at task 10(b): \"The stated training cutoff for this model is **June 2026**. In practice my dense, reliable knowledge of the Next.js changelog thins out around **December 2025 – January 2026**\". A density qualification, not a substitute date.",
    "believed_latest_version": "16.x; describes 16.1",
    "believed_latest_quote": "\"The most recent release whose *contents* I can describe is **16.1** (mid-December 2025: Turbopack file-system caching promoted, the Next.js DevTools MCP server, `images.maximumRedirects`, assorted Cache Components fixes) ... I have no reliable memory of a 16.2/16.3 feature list or a 17.\"",
    "believed_latest_quote_form": "draw",
    "boundary_note": "Equal to this subject's reading from code batteries (16.1.0) and to Claude Opus 5.5's ladder. P6 HELD on this arm — the only one of four. Its 16.1 content is partly misplaced: `images.maximumRedirects` shipped in 16.0.0 (this draw's own task 10 list for 16.0 omits it; its twin places it in 16.0). No hedged band content: it denied the disk-cache cap, the upstream body cap and the `transitionTypes` prop, and offered the dead `clientSegmentCache` key — so, unlike the Opus 5.5 pair, nothing in the tasks sits above the stated end.",
    "knowledge_stops_at_version": "16.1.0",
    "knowledge_stops_on": "2025-12-18",
    "knowledge_stops_provenance": "stated",
    "knowledge_gap_starts_at_version": "16.2.0",
    "knowledge_gap_starts_on": "2026-03-18",
    "knowledge_gap_provenance": "stated",
    "cutoff_lag_months": 6
  },
  "test": {
    "date": "2026-09-28",
    "battery": "next.js/v6-c",
    "battery_spec": "prompts/nextjs.md",
    "prompt_file": "prompts/sent/nextjs-v2.txt",
    "tasks": 9,
    "direct_questions": 2,
    "tasks_declined": 0,
    "elicits_code": true,
    "tool_uses_during_test": 0,
    "probe_window": {
      "from": "16.1.5",
      "to": "16.2.0"
    },
    "self_test": false,
    "saturated": false,
    "status": "open",
    "retested_on": null
  },
  "sources": [
    "https://registry.npmjs.org/next",
    "https://nextjs.org/blog/next-16-2"
  ],
  "summary": "Claude Fable 5.1 on the 16.2.0 window, re-sent `nextjs-v2.txt` byte-identical. Charged four times: an invented `images.maximumCacheSize` key written into both configs of task 5 (the build exits on it; the key is `maximumDiskCacheSize`, 16.1.7), the dead `experimental.clientSegmentCache: false` as the way to get one prefetch request per link (removed at 16.0.3; `prefetchInlining` since 16.2.0), Noto Sans as the OG image default (Geist since 16.2.0), and a React unknown-attribute warning predicted on the Pages Router for `Link transitionTypes`, which that router destructures away silently. Its twin agreed on all four. Stated boundary 16.1.0, the same as its code batteries — and, on the same bytes, it did the opposite of Claude Opus 5.5, which named three of those four correctly in hedges.",
  "findings": [
    {
      "id": "F1",
      "severity": "S1",
      "severity_label": "breaks-build",
      "title": "Writes `images.maximumCacheSize` to cap and to disable the optimized-image disk cache — an unrecognised `images` key, which stops the build; the key is `maximumDiskCacheSize`",
      "api": "images.maximumDiskCacheSize",
      "change_kind": "added",
      "introduced_in": "16.1.7",
      "introduced_on": "2026-03-16",
      "chargeable": true,
      "chargeable_note": "16.1.7 published 2026-03-16, three months before the stated June 2026 cutoff and three months after 16.1.0, the last release this draw says it can describe. The ladders measure minors only; prompts/nextjs.md § v6 decided before the draw that 16.1.x patches dated after 16.1.0 are live by date. Pre-registered charging arm and probe (task 5). CODE-VS-CLAIM RULE: the key is written into two code blocks, and \"Generated code that fails on the current version is always a finding, however well hedged\" — the draw's \"key name is a guess\" does not stop the block being pasted. Same shape as `opus-5-v2-a` F1 on these bytes, which invented the same key.",
      "model_belief": "Task 5(a): \"Honest answer: I don't know of a default disk-size cap on the optimized-image cache in any Next.js release I can describe ... If forced to guess at a rule: a percentage of the volume's free space (something like 50%), computed once at server startup. Treat that as a guess.\" Task 5(b): `maximumCacheSize: 1024 * 1024 * 1024, // 1 GB, bytes` (\"option name is a guess\"); 5(c): `maximumCacheSize: 0, // guess: 0 disables the disk cache`. Task 9: \"guessing. I'll commit to **16.1.0**\".",
      "wrong_code": "const nextConfig: NextConfig = {\n  images: {\n    remotePatterns: [{ protocol: 'https', hostname: 'cdn.example.com' }],\n    maximumCacheSize: 1024 * 1024 * 1024, // 1 GB, bytes\n  },\n}",
      "correct_code": "const nextConfig: NextConfig = {\n  images: {\n    remotePatterns: [{ protocol: 'https', hostname: 'cdn.example.com' }],\n    maximumDiskCacheSize: 1_000_000_000, // 0 disables disk caching\n  },\n}",
      "impact": "EXECUTED this session on the installed next 16.3.6: `configSchema.safeParse` on the draw's config returns `unrecognized_keys` at path `images`, key `maximumCacheSize`; `normalizeNextConfigZodErrors` (read in `dist/server/config.js`) marks every `images` issue fatal, so `loadConfig` throws 'Fatal next config errors found' and neither `next dev` nor `next build` starts. The same config with `maximumDiskCacheSize` parses clean. The 5(a) guess — about 50% of free space, computed once at startup — is the correct rule, given only as an undesignated guess under a designated 'no cap'. S1 as fixed in advance.",
      "citations": [
        {
          "url": "https://nextjs.org/docs/app/api-reference/components/image",
          "title": "Next.js docs — Image component, maximumDiskCacheSize",
          "published_on": "2026-09-02",
          "quote": "If no value is configured, the default behavior is to check the current available disk space once during startup and use 50%."
        },
        {
          "url": "https://registry.npmjs.org/next",
          "title": "Executed against the published package (next 16.3.6, installed this session)",
          "published_on": "2026-09-28",
          "quote": "images.maximumCacheSize: unrecognized_keys at path images (fatal). images.maximumDiskCacheSize: 1000000000 and 0: OK."
        }
      ]
    },
    {
      "id": "F2",
      "severity": "S2",
      "severity_label": "silently-wrong",
      "title": "Recommends `experimental.clientSegmentCache: false` for one prefetch request per link — the key was removed at 16.0.3 and is now only warned about; the option is `experimental.prefetchInlining`",
      "api": "experimental.clientSegmentCache",
      "change_kind": "removed",
      "introduced_in": "16.0.3",
      "introduced_on": "2025-11-13",
      "chargeable": true,
      "chargeable_note": "Removed 2025-11-13, seven months before the stated cutoff and a month BELOW the 16.1.0 this draw says it describes, so it is well inside the window. Pre-registered: \"task 8 offering `experimental.clientSegmentCache` charges LF28 S2\". DESIGNATION: \"Yes. ... Reverting to one request per link means turning that cache off\" with the key in the only code block; `prefetch={false}` is offered only as the fallback if the toggle is refused. The first LF28 charge on Claude Fable 5.1 (its `v4` runs were a non-charging calibration).",
      "model_belief": "\"Yes. The burst is the **Segment Cache** (the 16-era client router that ships with `cacheComponents` and can be enabled alone via `experimental.clientSegmentCache`) ... Reverting to one request per link means turning that cache off and going back to the whole-route prefetch\" — `experimental: { clientSegmentCache: false }`. \"I do not know of an option that keeps the segment cache but coalesces its requests into one.\"",
      "wrong_code": "const config: NextConfig = {\n  experimental: {\n    clientSegmentCache: false,\n  },\n}",
      "correct_code": "const config: NextConfig = {\n  experimental: {\n    prefetchInlining: true,\n  },\n}",
      "impact": "EXECUTED this session on the installed next 16.3.6: `configSchema` reports `unrecognized_keys` at path `experimental`, key `clientSegmentCache`, and `normalizeNextConfigZodErrors` files an unrecognised `experimental` key as a WARNING unless it names one of three listed migrations — so the app starts, prints 'Invalid next.config options detected', and per-segment prefetching carries on exactly as before. The team believes it has traded duplication for fewer requests and has done neither. `experimental.prefetchInlining: true` parses clean and is the lever the task describes. S2 as fixed in advance.",
      "citations": [
        {
          "url": "https://unpkg.com/next@16.0.3/dist/server/config-shared.d.ts",
          "title": "next 16.0.3 published package — the key is gone one day after 16.0.2",
          "published_on": "2025-11-13",
          "quote": "(no occurrence of clientSegmentCache in the file)"
        },
        {
          "url": "https://nextjs.org/blog/next-16-2",
          "title": "Next.js 16.2 release post — experimental.prefetchInlining",
          "published_on": "2026-03-18",
          "quote": "The new experimental.prefetchInlining option bundles all segment data for a route into a single response, reducing the number of prefetch requests to one per link."
        },
        {
          "url": "https://registry.npmjs.org/next",
          "title": "Executed against the published package (next 16.3.6, installed this session)",
          "published_on": "2026-09-28",
          "quote": "experimental.clientSegmentCache: unrecognized_keys at path experimental (warning). experimental.prefetchInlining: true: OK."
        }
      ]
    },
    {
      "id": "F3",
      "severity": "S2",
      "severity_label": "silently-wrong",
      "title": "Names Noto Sans — down to the bundled filename — as the OG image default font; since 16.2.0 it is Geist Sans",
      "api": "ImageResponse default font",
      "change_kind": "behavior-changed",
      "introduced_in": "16.2.0",
      "introduced_on": "2026-03-18",
      "chargeable": true,
      "chargeable_note": "16.2.0 published 2026-03-18, three months before the stated cutoff; live (`+`) for Claude Fable 5.1 in charge-windows.mjs. Pre-registered probe (task 3). Designated without a hedge: \"Confidence: high on Noto Sans Regular\". P1 HELD on this arm.",
      "model_belief": "\"**Noto Sans**, weight 400 (Regular), Latin subset. `next/og` is a vendored copy of `@vercel/og`, which bundles `noto-sans-v27-latin-regular.ttf` as its built-in font ... Confidence: high on Noto Sans Regular\". Task 9 dated it to 13.3.0 (April 2023).",
      "impact": "The filename is exactly right for 16.1.7 and exactly wrong from 16.2.0: the current 16.3.6 bundles `Geist-Regular.ttf` (read this session) and no Noto Sans file at all. OG cards laid out against Noto Sans metrics render in Geist and nothing warns. S2 as fixed in advance.",
      "citations": [
        {
          "url": "https://nextjs.org/blog/next-16-2",
          "title": "Next.js 16.2 release post — Faster ImageResponse",
          "published_on": "2026-03-18",
          "quote": "Default font changed from Noto Sans to Geist Sans"
        },
        {
          "url": "https://registry.npmjs.org/next",
          "title": "Read in the published packages this session (next 16.1.6 / 16.2.0 / 16.3.5 / 16.3.6)",
          "published_on": "2026-09-28",
          "quote": "16.1.6: noto-sans-v27-latin-regular.ttf. 16.2.0, 16.3.5, 16.3.6: Geist-Regular.ttf."
        }
      ]
    },
    {
      "id": "F4",
      "severity": "S2",
      "severity_label": "silently-wrong",
      "title": "Says the Pages Router `Link` spreads `transitionTypes` onto the `<a>` and React warns about an unknown attribute — that router destructures the prop away and ignores it silently",
      "api": "Link transitionTypes",
      "change_kind": "added",
      "introduced_in": "16.2.0",
      "introduced_on": "2026-03-18",
      "chargeable": true,
      "chargeable_note": "16.2.0, three months before the stated cutoff. Pre-registered probe (task 4). DESIGNATION: parts (b) and (c) offer two forms and then designate one — \"It would either be listed in its known-prop table and ignored (no-op), or — more likely if it's App-Router-only — fall through the rest-props spread onto the `<a>` element ... My best guess: warning in Pages Router.\" The charge follows the designated form (HARNESS clause 2); the no-op branch is published and charges nothing. Narrower than `opus-5-v2-a` F4, which denied the prop in both routers: this draw has the App Router half right.",
      "model_belief": "\"(b) Pages Router: the Pages Router `Link` is a different implementation and has no view-transition integration. It would either be listed in its known-prop table and ignored (no-op), or — more likely if it's App-Router-only — fall through the rest-props spread onto the `<a>` element as an unknown attribute.\" \"(c) ... Pages Router — if the prop is not in that `Link`'s recognized list, React warns in development: 'React does not recognize the `transitionTypes` prop on a DOM element…' ... My best guess: warning in Pages Router.\" (a) App Router and (d) the dev-time array error were right.",
      "impact": "Read this session in next 16.3.6's Pages Router `dist/client/link.js`: the props destructuring lists `transitionTypes` before `...restProps`, so the prop never reaches the `<a>` and React has nothing to warn about. The 16.2 release post says so in terms: shared link components work across both routers. A team told otherwise forks its NavLink per router or strips the prop by hand for a warning that does not exist. S2 as fixed in advance.",
      "citations": [
        {
          "url": "https://nextjs.org/blog/next-16-2",
          "title": "Next.js 16.2 release post — transitionTypes Prop for next/link",
          "published_on": "2026-03-18",
          "quote": "transitionTypes on Pages Router links is silently ignored, so shared link components work across both routers."
        },
        {
          "url": "https://registry.npmjs.org/next",
          "title": "next 16.3.6 published package — dist/client/link.js (the Pages Router Link), read this session",
          "published_on": "2026-09-28",
          "quote": "legacyBehavior = false, transitionTypes, ...restProps } = props;"
        }
      ]
    }
  ],
  "non_findings": [
    {
      "kind": "miss",
      "chargeable_miss": true,
      "miss_class": "no_severity_level",
      "charged_on": null,
      "summary": "Task 1(a): hand-rolled `router.refresh()` + `reset()` in `startTransition`, with no mention of a built-in retry (`unstable_retry` since 16.2.0, `retry` since 16.3.0). Working code; not charged (`next.js/v2` precedent).",
      "api": "error.tsx retry prop",
      "introduced_in": "16.2.0",
      "why_not_a_finding": "The hand-rolled code works on 16.3.6."
    },
    {
      "kind": "miss",
      "chargeable_miss": true,
      "miss_class": "no_severity_level",
      "charged_on": null,
      "summary": "Task 2(a): \"Next.js doesn't export a public component-level error boundary\" — a hand-written React class boundary with `unstable_rethrow` in `getDerivedStateFromError`. `next/error` has exported one since 16.2.0. Working code; not charged.",
      "api": "catchError (next/error)",
      "introduced_in": "16.2.0",
      "why_not_a_finding": "The class boundary with `unstable_rethrow` isolates the widget and passes redirects through."
    },
    {
      "kind": "context",
      "summary": "DERIVABLE, both: task 1(b) (reset re-renders the held payload, no request, the query does not re-run) and task 2(b) (a naive boundary swallows `NEXT_REDIRECT`; `unstable_rethrow` fixes it, with the full-document 307 caveat). Correct and detailed; answered by both v2 controls.",
      "chargeable_miss": false
    },
    {
      "kind": "context",
      "summary": "VOID PROBE — task 6, scored for nobody. This draw took the allowlist as satisfied and designated \"the original 80 MB JPEG, byte-for-byte, unoptimized\" via the optimizer's upstream fallback, stating \"there is no default byte-size cap I know of\". On 16.1.5+ the optimizer streams the body and throws a 413 past 50 MB (LF26). Recorded, not charged, because the probe's wording is void on these bytes.",
      "api": "images.maximumResponseBody",
      "introduced_in": "16.1.5",
      "chargeable_miss": false
    },
    {
      "kind": "imprecision",
      "summary": "Task 7, THE INTERNAL CONTROL, WRONG ON THE MECHANISM: \"`quality={90}` is not in the allowed list, so the image is **not served at 90 — it is not served at all**\" — a dev-time throw and a production 400 — adding \"medium that the component does not snap to the nearest allowed value\". EXECUTED on 16.3.6: the default loader emits `q=75` for `quality: 90` (it calls `findClosestQuality`), and development only `warnOnce`s. The server's 400 for an unlisted `q` is real but unreachable through `next/image`. Recorded as an imprecision, not charged, under the v1 code-vs-claim rule that recorded the same '400' claim for Claude Sonnet 5, Claude Fable 5 and Claude Opus 5: hedged, and the fix it names (`qualities: [75, 90]`) is right. The release (16.0.0, 21 October 2025) is correct, so attribution is readable.",
      "api": "images.qualities",
      "introduced_in": "16.0.0",
      "chargeable_miss": false
    },
    {
      "kind": "context",
      "summary": "Task 9, attribution: the OG font 'inherited from @vercel/og' at 13.3.0 / 14.0.0; the disk-cache cap \"in a **16.2.0**-era minor, roughly February–March 2026\" — two days late (true 16.1.7), for a feature the same draw's task 5 said it could not describe. No patch named. P5 HELD.",
      "chargeable_miss": false
    }
  ],
  "open_questions": [
    {
      "question": "On identical bytes, Claude Opus 5.5 stated a LOWER boundary (16.0) than Claude Fable 5.1 (16.1) and produced MORE band content in hedges (prefetchInlining, the right disk-cache key, the ~50 MB body cap, unstable_retry), while Fable 5.1 denied or invented every one. Both state June 2026. Is self-reported next.js boundary anti-correlated with hedged recall here, or is Opus 5.5 simply more willing to guess and luckier? n=2 per subject, one prompt.",
      "status": "open"
    }
  ]
}