{
  "$schema": "../../schema/run.schema.json",
  "run_id": "react-router--claude-opus-5--v1-c--2026-09-09",
  "supersedes": null,
  "replicate_of": null,
  "library": {
    "name": "react-router",
    "ecosystem": "npm",
    "latest_version_at_test": "8.3.1",
    "latest_version_verified_on": "2026-09-09",
    "latest_version_note": "`https://registry.npmjs.org/react-router` read this session before the prompt was written: `dist-tags.latest` is 8.3.1, `version-7` is 7.18.3, `version-6` is 6.30.6. Three real installs were driven this session, each under the package's real name in its own scratch directory beside `react@19.2.8`: `react-router@7.11.0`, `@7.14.2` and `@8.3.1`. Every claim scored below was executed against them, not read off a changelog."
  },
  "model": {
    "id": "claude-opus-5",
    "label": "Claude Opus 5",
    "vendor": "Anthropic",
    "invoked_as": "Agent tool, model alias \"opus\"; prompt sent verbatim from prompts/sent/react-router-v1.txt. Pre-registered as the second charging subject, run single (LF1 is its only live fact; LF2 and LF3 are parked in its cutoff month). This is the only arm of four that is licensed to charge anything.",
    "self_reported_cutoff": "2026-05",
    "cutoff_basis": "Self-reported, AFFIRMING the stated date and qualifying only the density of recall: \"My stated training cutoff is **May 2026**. For this library specifically my usable detail thins out sharply after roughly mid-2025, so treat anything I say about late-2025 or 2026 releases as unreliable. That gap between stated cutoff and actual recall is itself worth noting for your measurement.\" Applying HARNESS.md's distinguishing test — does the answer qualify the subject's recall, or does it choose between two dates? — this qualifies: it names May 2026 as the cutoff, describes how reliable its *content* recall is above mid-2025, and frames the difference as \"the gap between stated cutoff and actual recall\", which preserves the stated date as the cutoff rather than replacing it. It never offers a second date as the cutoff and never uses the word trust. Contrast both Fable 5.1 arms in this same battery, on this same prompt, which did offer one and are therefore disqualified.",
    "believed_latest_version": "7.9.x",
    "believed_latest_quote": "\"The most recent version I can describe with reasonable confidence is **React Router 7.9.x, around September 2025** — the release I associate with middleware being stabilized behind a `future.v8_middleware` flag. That is also the highest number I'd assert as real from memory. ... So: no clean gap between 'latest I know of' and 'latest I can describe' here — my knowledge just stops, which likely means I'm behind.\"\n\nBRACKET PROVENANCE — Both ends come from direct question (c), asked last. It described 7.9.0's contents and dated it to September 2025 (actual 2025-09-12), then named 7.10.0 as \"the first release I know only as a number, not contents\". The self-placement is unusually explicit — \"my knowledge just stops, which likely means I'm behind\" — and it declined to assert any release above 7.9.0 as real.",
    "knowledge_stops_at_version": "7.9.0",
    "knowledge_stops_on": "2025-09-12",
    "knowledge_gap_starts_at_version": "7.10.0",
    "knowledge_gap_starts_on": "2025-12-02",
    "cutoff_lag_months": 8
  },
  "test": {
    "date": "2026-09-09",
    "battery": "react-router/v1-c",
    "battery_spec": "prompts/react-router.md",
    "prompt_file": "prompts/sent/react-router-v1.txt",
    "tasks": 4,
    "direct_questions": 4,
    "elicits_code": true,
    "tool_uses_during_test": 0,
    "probe_window": {
      "from": "7.12.0",
      "to": "7.15.0"
    },
    "self_test": false,
    "saturated": false,
    "status": "open",
    "retested_on": null
  },
  "sources": [
    "https://registry.npmjs.org/react-router",
    "https://github.com/remix-run/react-router/blob/main/packages/react-router/CHANGELOG.md",
    "https://github.com/remix-run/react-router/pull/14269"
  ],
  "findings": [
    {
      "id": "F1",
      "severity": "S2",
      "severity_label": "silently-wrong",
      "title": "States as current behaviour that the path helper silently returns the pattern unsubstituted, and ships a workaround for a footgun the library removed eight months ago",
      "api": "generatePath",
      "change_kind": "behavior-changed",
      "introduced_in": "7.12.0",
      "introduced_on": "2026-01-07",
      "chargeable": true,
      "chargeable_note": "react-router 7.12.0 published 2026-01-07, four months inside this subject's stated May 2026 cutoff, which it affirmed in direct question (b) while qualifying only the density of its recall. This is the Index's first charged finding on react-router and the first measured boundary on the library.",
      "model_belief": "Asked for the concrete URL and then, separately, whether there is anything about the pattern shape worth knowing, it answered in the present tense: \"generatePath(\\\"/books/:id.json\\\", { id: \\\"7\\\" });\" produces \"/books/:id.json\" — \"Not `/books/7.json`. It silently returns the pattern back, unsubstituted — no throw, no warning.\" It then explained the mechanism it believes is current: \"`generatePath` interpolates **whole path segments only**. Its implementation splits the pattern on `/` and tests each segment against an anchored regex along the lines of `^:([\\w-]+)\\??$`. `:id.json` is a param *plus a literal suffix*, so the segment fails that test and is passed through verbatim.\" It called the resulting asymmetry between matching and generating \"a real footgun\" and shipped a workaround as the code it would ship.",
      "wrong_code": "// The code the draw says it would actually ship, and the reason it gives for it.\n// app/lib/paths.ts\nimport { generatePath } from \"react-router\";\n\nexport const BOOK_JSON = \"/books/:id.json\";           // still the single source of truth\nexport const bookJsonPath = (id: string) =>\n  `${generatePath(\"/books/:id\", { id })}.json`;        // -> \"/books/7.json\"\n\n// Its first recommendation is to change the URL rather than call the helper:\n//   \"Restructure the route to /books/:id/export.json (or .../data.json) so the param\n//    is a whole segment. Then generatePath — and, in framework mode, the typed href()\n//    — just work.\"",
      "correct_code": "import { generatePath } from \"react-router\";\n\n// Executed this session against react-router@8.3.1, installed under its real name\n// beside react@19.2.8:\n//   generatePath(\"/books/:id.json\", { id: \"7\" })  ->  \"/books/7.json\"\n// and against react-router@7.11.0, the release below the boundary:\n//   generatePath(\"/books/:id.json\", { id: \"7\" })  ->  \"/books/:id.json\"\n// The draw describes 7.11.0's behaviour and states it as current.\nexport const BOOK_JSON = \"/books/:id.json\";\nexport const bookJsonPath = (id: string) => generatePath(BOOK_JSON, { id });\n\n// href() was ALSO executed at all three rungs and returns \"/books/7.json\" at\n// 7.11.0, 7.14.2 and 8.3.1 — it never had this problem in the tested window.",
      "impact": "A developer is told, in the present tense and with a mechanism, that the router's own path helper cannot build this URL. The concrete costs are all in the draw's own answer: its first recommendation is to **change the application's public URLs** so the param becomes a whole segment; its second is a hand-written concatenation helper plus a unit test written to catch \"a router upgrade that changes this behavior\" — an upgrade that happened eight months before the question was asked; and its third is to abandon the path suffix for content negotiation. A URL scheme redesigned around a fixed bug is not recoverable by a later `npm update`. The generated code does produce the right string, which is what caps this at S2 rather than S1.",
      "citations": [
        {
          "url": "https://github.com/remix-run/react-router/blob/main/packages/react-router/CHANGELOG.md",
          "title": "react-router CHANGELOG — 7.12.0",
          "published_on": "2026-01-07"
        },
        {
          "url": "https://registry.npmjs.org/react-router",
          "title": "react-router 8.3.1 and 7.11.0, shipped packages — `generatePath` executed at both",
          "published_on": "2026-09-09",
          "quote": "/books/7.json"
        }
      ],
      "scope_note": "Charged on the present-tense claim about `generatePath` only. Two subsidiary claims are separated out. (1) Its account of the OLD mechanism is accurate — 7.11.0 does return the pattern verbatim with no throw and no warning, verified this session — so the finding is that the belief is stale, not that it was ever wrong. (2) Its claim about the typed helper, \"Note `href()` ... is built on the same segment-wise interpolation, so I would not expect it to rescue a partial segment either\", is FALSE at every rung tested: `href(\"/books/:id.json\", { id: \"7\" })` returns `\"/books/7.json\"` at 7.11.0, 7.14.2 and 8.3.1. It is not charged separately because the draw explicitly hedged it and told the developer to check — \"worth a 30-second check against your version rather than trusting me\" — which is an imprecision under the code-vs-claim rule, not a finding. Its claim that matching handles the pattern is also correct and is not charged."
    }
  ],
  "non_findings": [
    {
      "kind": "imprecision",
      "summary": "Task 2's one-word answer is \"no\" — the router provides no dedicated instrumentation hook — and the instrumentation API has existed in `unstable_` form since a 7.9.x patch, well inside this subject's cutoff. It is not charged, for two independent reasons and both are structural rather than generous. First, the only published fact covering this API is LF3, dated to the 7.15.0 stabilisation (2026-05-05), which is inside this subject's stated cutoff MONTH and therefore parked. Second, the draw hedged onto the true option and named it: \"I have a faint, low-confidence sense that an `unstable_instrumentation`-style API was discussed for tracing loaders/actions with route ids; if your version is newer than mid-2025, check the changelog before building the manual version.\" Under the code-vs-claim rule that is an imprecision, and under HARNESS.md § *The hedge lands on the true option* it is the pattern already recorded twice.",
      "api": "instrumentations",
      "introduced_in": "7.15.0",
      "chargeable_miss": true,
      "miss_class": "stated_cutoff",
      "charged_on": null,
      "why_not_a_finding": "LF3's release is parked in this subject's stated cutoff month, and the draw hedged onto the correct API by name."
    },
    {
      "kind": "imprecision",
      "summary": "Task 3 reads the URL with `new URL(request.url)` and never mentions the normalised `url` argument the loader has received since 7.15.0 (LF2). Working code, and the additive-API rule makes it an imprecision rather than a finding: it did not claim no such argument exists. LF2 is parked for this subject in any case. Its list of ways the loader's URL can differ from the address bar is unusually good and mostly correct — prefetch and fetcher loads running for URLs the user is not on, the hash never reaching the server, proxies rewriting the origin, `clientLoader` synthesising the Request.",
      "api": "url",
      "introduced_in": "7.15.0"
    },
    {
      "kind": "correct",
      "summary": "THE ATTRIBUTION ANCHOR, and it is exact. Task 4 produced a working framework-mode scaffold — `@react-router/dev/vite` plugin, `react-router.config.ts` typed with `Config`, `app/routes.ts` using `index`/`route`/`layout`/`prefix`, a route module with `Route.LoaderArgs`/`Route.ComponentProps` from `./+types/`, and the `rootDirs` typegen wiring — and in direct question (c) dated 7.0.0 to \"Nov 22, 2024\", which is the exact publication date. An arm that places the anchor to the day is readable, and its boundary answer counts.",
      "api": null,
      "introduced_in": "7.0.0"
    },
    {
      "kind": "context",
      "summary": "The poison rung produced no false positive and no discrimination, which is the honest reading. `7.19.0` has never been published and this arm declined it — but it declined every number above 7.9.0, real ones included, and said so explicitly: \"I can only positively vouch for 7.5.0 and 7.9.0. For every 8.x number and every 7.x above 7.9, 'I don't know' is the accurate answer, not 'that doesn't exist.'\" Per HARNESS.md § *An abstention is not a denial*, that is a subject declining to guess above its own boundary rather than a subject discriminating a fake from a real release. What the rung does establish is the thing it exists for: nothing in this arm's version answers is confabulated, so its (c) answer can be read as a boundary.",
      "api": null,
      "introduced_in": null
    },
    {
      "kind": "context",
      "summary": "THE PREDICTION IS CONFIRMED ON THIS ARM AND THE SPEC CALLED THE WEAKNESS IN ADVANCE. Predicted: a boundary later than this subject's 2025-08-23 median across the seven measured libraries. Measured: 7.9.0, 2025-09-12 — later, by twenty days. `prompts/react-router.md` pre-registered exactly this outcome as a weak confirmation: \"react-router published only three minors in the whole of 2025 H2 and nothing at all between 2025-09-12 and 2025-12-02 — an 81-day gap sitting directly on Opus 5's median. A boundary that lands at 7.9.0 is only 20 days above the median and should be reported as a weak confirmation, not a strong one.\" It landed on 7.9.0. Read against the two Fable 5.1 arms, which the same prediction FALSIFIED at the same release, the twenty days are better explained by the release gap than by the loud-library mechanism.",
      "api": null,
      "introduced_in": null
    }
  ],
  "open_questions": [
    {
      "question": "Does `href()` substitute a param followed by a literal suffix at every release, or does it have a boundary of its own below 7.9.0? (Why it matters: It is the correct answer this battery hands developers on both sides of LF1's boundary, and it is currently measured at three rungs (7.11.0, 7.14.2, 8.3.1) rather than across the bisector's ladder. If it is an invariant it is worth a fact of its own with `change_kind: invariant`; three rungs is not enough to publish one.)",
      "status": "open"
    }
  ],
  "summary": "The only arm of four licensed to charge, and it charges once. Claude Opus 5 affirmed its May 2026 cutoff while qualifying recall density — the qualifying side of the line both Fable 5.1 arms fell off — and then stated, in the present tense and with a mechanism, that `generatePath` silently returns `/books/:id.json` unsubstituted. react-router 7.12.0 fixed that on 2026-01-07, four months inside its cutoff; the shipped 8.3.1 package returns `/books/7.json` and 7.11.0 returns the pattern, both executed this session. Charged S2: the code works, but the advice built on it is to redesign the application's URLs and to write a regression test against an upgrade that already happened. Boundary 7.9.0 / 7.10.0 — the Index's first measured boundary on react-router — and the battery's prediction is confirmed here by twenty days, the weak confirmation its spec named in advance."
}