docs(fern): fix redirects so Sphinx URLs actually resolve (#1310)

## Summary
- All 11 unique `docs.nvidia.com/nemo/gym/*.html` links from `README.md`
were returning **404** with no redirect on the production Fern preview
(`https://nvidia-gym.docs.buildwithfern.com/`).
- Root cause: with `experimental.basepath-aware: true`, Fern requires
the full `/nemo/gym/` basepath with a leading slash on **both** source
and destination of every redirect rule (verified by comparing to
nemo-curator's working `docs.yml`). Our block had two systematic issues:
1. Legacy Sphinx sources omitted the leading slash (`nemo/gym/foo.html`)
→ never matched.
2. Most destinations omitted the basepath (`/latest/foo`) → matched but
emitted a `Location` outside the basepath, still 404.
- Mirrors nemo-curator's pattern, and adds 3 explicit redirects for
pages renamed during the Fern migration: `unsloth-training` → `unsloth`,
`apidocs` → `api/reference/api-reference`,
`creating-training-environment` → `single-step-environment`.

## Test plan
- [x] Local trace of all 11 README URLs through the new rule table —
every URL resolves to a canonical Fern path.
- [x] Spot-checked the resolved canonicals against the live preview —
10/11 are 200. (`training-tutorials/verl` is a stale-deploy issue,
separate from redirects.)
- [ ] **Post-merge**: redeploy and run `curl -sI <old-url>` against each
old Sphinx URL; expect `308` + a `Location:` header pointing at the
canonical Fern path.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Signed-off-by: Lawrence Lane <llane@nvidia.com>
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: lbliii

fern/docs.yml

@@ -76,89 +76,111 @@ versions:
     availability: stable
 
 redirects:
-  # Generated by utils/generate_redirects.py — re-run from repo root; see scripts README
-  - source: "nemo/gym/index.html"
-    destination: "/main"
-  - source: "nemo/gym/index"
-    destination: "/main"
-  - source: "nemo/gym/about/concepts/configuration-system.html"
-    destination: "/about/concepts/configuration"
-  - source: "nemo/gym/about/concepts/core-abstractions.html"
-    destination: "/about/core-components"
-  - source: "nemo/gym/get-started/setup-installation.html"
-    destination: "/get-started/installation"
-  - source: "/latest/get-started/detailed-setup"
-    destination: "/latest/get-started/quickstart"
-  - source: "/latest/get-started/rollout-collection"
-    destination: "/latest/get-started/quickstart"
-  - source: "nemo/gym/how-to-faq.html"
-    destination: "/reference/faq"
-  - source: "nemo/gym/infrastructure/aiohttp-vs-httpx.html"
-    destination: "/infrastructure/engineering-notes/aiohttp-vs-httpx"
-  - source: "nemo/gym/infrastructure/swe-rl-case-study.html"
-    destination: "/infrastructure/engineering-notes/swe-rl-case-study"
-  - source: "nemo/gym/training/rl-framework-integration/generation-backend-and-openai-compatible-http-server.html"
-    destination: "/contribute/rl-framework-integration/generation-backend-and-openai-compatible-http-server"
-  - source: "nemo/gym/training/rl-framework-integration/gym-integration-footprint-and-form-factor.html"
-    destination: "/contribute/rl-framework-integration/gym-integration-footprint-and-form-factor"
-  - source: "nemo/gym/training/rl-framework-integration/gym-rl-framework-integration-success-criteria.html"
-    destination: "/contribute/rl-framework-integration/gym-rl-framework-integration-success-criteria"
-  - source: "nemo/gym/training/rl-framework-integration/index.html"
-    destination: "/contribute/rl-framework-integration"
-  - source: "nemo/gym/training/rl-framework-integration/integration-footprint.html"
-    destination: "/contribute/rl-framework-integration/gym-integration-footprint-and-form-factor"
-  - source: "nemo/gym/training/rl-framework-integration/on-policy-corrections.html"
-    destination: "/contribute/rl-framework-integration/openai-compatible-http-server-on-policy-correction"
-  - source: "nemo/gym/training/rl-framework-integration/openai-compatible-http-server-on-policy-correction.html"
-    destination: "/contribute/rl-framework-integration/openai-compatible-http-server-on-policy-correction"
-  - source: "nemo/gym/tutorials/creating-resource-server.html"
-    destination: "/environment-tutorials/single-step-environment"
-  - source: "nemo/gym/tutorials/index.html"
-    destination: "/training-tutorials"
-  - source: "nemo/gym/tutorials/nemo-rl-grpo/about-workplace-assistant.html"
-    destination: "/training-tutorials/nemo-rl-grpo/about-workplace-assistant"
-  - source: "nemo/gym/tutorials/nemo-rl-grpo/gym-configuration.html"
-    destination: "/training-tutorials/nemo-rl-grpo/gym-configuration"
-  - source: "nemo/gym/tutorials/nemo-rl-grpo/index.html"
-    destination: "/training-tutorials/nemo-rl-grpo"
-  - source: "nemo/gym/tutorials/nemo-rl-grpo/multi-node-training.html"
-    destination: "/training-tutorials/nemo-rl-grpo/multi-node-training"
-  - source: "nemo/gym/tutorials/nemo-rl-grpo/nemo-rl-configuration.html"
-    destination: "/training-tutorials/nemo-rl-grpo/nemo-rl-configuration"
-  - source: "nemo/gym/tutorials/nemo-rl-grpo/setup.html"
-    destination: "/training-tutorials/nemo-rl-grpo/setup"
-  - source: "nemo/gym/tutorials/nemo-rl-grpo/single-node-training.html"
-    destination: "/training-tutorials/nemo-rl-grpo/single-node-training"
-  - source: "nemo/gym/tutorials/offline-training-w-rollouts.html"
-    destination: "/training-tutorials/offline-training-w-rollouts"
-  - source: "/latest/about/concepts/core-components"
-    destination: "/latest/about/core-components"
-  - source: "/latest/about/concepts/architecture"
-    destination: "/latest/infrastructure/engineering-notes/system-design"
-  - source: "/latest/about/concepts/task-verification"
-    destination: "/latest/resources-server"
-  - source: "/latest/about/concepts/configuration"
-    destination: "/latest/reference/configuration"
-  - source: "/latest/environment-tutorials/designing-customer-evaluation"
-    destination: "/latest/environment-tutorials"
-  - source: "/v0.2.1/environment-tutorials/real-world-data-generation"
-    destination: "/v0.2.1/environment-tutorials/real-world-environment/generating-training-data"
-  - source: "/v0.2.1/environment-tutorials/real-world-implementation"
-    destination: "/v0.2.1/environment-tutorials/real-world-environment/resources-server-implementation"
-  - source: "/latest/environment-tutorials/real-world-data-generation"
-    destination: "/latest/environment-tutorials/real-world-environment/generating-training-data"
-  - source: "/latest/environment-tutorials/real-world-implementation"
-    destination: "/latest/environment-tutorials/real-world-environment/resources-server-implementation"
-  - source: "/v0.2/:path*"
-    destination: "/v0.2.1/:path*"
-  - source: "nemo/gym/latest/:path*/index.html"
+  # With `experimental.basepath-aware: true`, both source and destination must include
+  # the full `/nemo/gym/` basepath with a leading slash. See nemo-curator's docs.yml.
+  # Legacy Sphinx top-level entry points (Main is now the default version)
+  - source: "/nemo/gym/index.html"
+    destination: "/nemo/gym/main"
+  - source: "/nemo/gym/index"
+    destination: "/nemo/gym/main"
+  # Legacy Sphinx page paths → current Fern slugs
+  - source: "/nemo/gym/about/concepts/configuration-system.html"
+    destination: "/nemo/gym/about/concepts/configuration"
+  - source: "/nemo/gym/about/concepts/core-abstractions.html"
+    destination: "/nemo/gym/about/core-components"
+  - source: "/nemo/gym/get-started/setup-installation.html"
+    destination: "/nemo/gym/get-started/installation"
+  - source: "/nemo/gym/how-to-faq.html"
+    destination: "/nemo/gym/reference/faq"
+  - source: "/nemo/gym/infrastructure/aiohttp-vs-httpx.html"
+    destination: "/nemo/gym/infrastructure/engineering-notes/aiohttp-vs-httpx"
+  - source: "/nemo/gym/infrastructure/swe-rl-case-study.html"
+    destination: "/nemo/gym/infrastructure/engineering-notes/swe-rl-case-study"
+  - source: "/nemo/gym/training/rl-framework-integration/generation-backend-and-openai-compatible-http-server.html"
+    destination: "/nemo/gym/contribute/rl-framework-integration/generation-backend-and-openai-compatible-http-server"
+  - source: "/nemo/gym/training/rl-framework-integration/gym-integration-footprint-and-form-factor.html"
+    destination: "/nemo/gym/contribute/rl-framework-integration/gym-integration-footprint-and-form-factor"
+  - source: "/nemo/gym/training/rl-framework-integration/gym-rl-framework-integration-success-criteria.html"
+    destination: "/nemo/gym/contribute/rl-framework-integration/gym-rl-framework-integration-success-criteria"
+  - source: "/nemo/gym/training/rl-framework-integration/index.html"
+    destination: "/nemo/gym/contribute/rl-framework-integration"
+  - source: "/nemo/gym/training/rl-framework-integration/integration-footprint.html"
+    destination: "/nemo/gym/contribute/rl-framework-integration/gym-integration-footprint-and-form-factor"
+  - source: "/nemo/gym/training/rl-framework-integration/on-policy-corrections.html"
+    destination: "/nemo/gym/contribute/rl-framework-integration/openai-compatible-http-server-on-policy-correction"
+  - source: "/nemo/gym/training/rl-framework-integration/openai-compatible-http-server-on-policy-correction.html"
+    destination: "/nemo/gym/contribute/rl-framework-integration/openai-compatible-http-server-on-policy-correction"
+  - source: "/nemo/gym/tutorials/creating-resource-server.html"
+    destination: "/nemo/gym/environment-tutorials/single-step-environment"
+  - source: "/nemo/gym/tutorials/index.html"
+    destination: "/nemo/gym/training-tutorials"
+  - source: "/nemo/gym/tutorials/nemo-rl-grpo/about-workplace-assistant.html"
+    destination: "/nemo/gym/training-tutorials/nemo-rl-grpo/about-workplace-assistant"
+  - source: "/nemo/gym/tutorials/nemo-rl-grpo/gym-configuration.html"
+    destination: "/nemo/gym/training-tutorials/nemo-rl-grpo/gym-configuration"
+  - source: "/nemo/gym/tutorials/nemo-rl-grpo/index.html"
+    destination: "/nemo/gym/training-tutorials/nemo-rl-grpo"
+  - source: "/nemo/gym/tutorials/nemo-rl-grpo/multi-node-training.html"
+    destination: "/nemo/gym/training-tutorials/nemo-rl-grpo/multi-node-training"
+  - source: "/nemo/gym/tutorials/nemo-rl-grpo/nemo-rl-configuration.html"
+    destination: "/nemo/gym/training-tutorials/nemo-rl-grpo/nemo-rl-configuration"
+  - source: "/nemo/gym/tutorials/nemo-rl-grpo/setup.html"
+    destination: "/nemo/gym/training-tutorials/nemo-rl-grpo/setup"
+  - source: "/nemo/gym/tutorials/nemo-rl-grpo/single-node-training.html"
+    destination: "/nemo/gym/training-tutorials/nemo-rl-grpo/single-node-training"
+  - source: "/nemo/gym/tutorials/offline-training-w-rollouts.html"
+    destination: "/nemo/gym/training-tutorials/offline-training-w-rollouts"
+  # Renamed/moved pages within the Fern site
+  - source: "/nemo/gym/latest/get-started/detailed-setup"
+    destination: "/nemo/gym/latest/get-started/quickstart"
+  - source: "/nemo/gym/latest/get-started/rollout-collection"
+    destination: "/nemo/gym/latest/get-started/quickstart"
+  - source: "/nemo/gym/latest/about/concepts/core-components"
+    destination: "/nemo/gym/latest/about/core-components"
+  - source: "/nemo/gym/latest/about/concepts/architecture"
+    destination: "/nemo/gym/latest/infrastructure/engineering-notes/system-design"
+  - source: "/nemo/gym/latest/about/concepts/task-verification"
+    destination: "/nemo/gym/latest/resources-server"
+  - source: "/nemo/gym/latest/about/concepts/configuration"
+    destination: "/nemo/gym/latest/reference/configuration"
+  - source: "/nemo/gym/latest/about/concepts/training-approaches"
+    destination: "/nemo/gym/latest/about/concepts/training"
+  - source: "/nemo/gym/latest/environment-tutorials/designing-customer-evaluation"
+    destination: "/nemo/gym/latest/environment-tutorials"
+  - source: "/nemo/gym/v0.2.1/environment-tutorials/real-world-data-generation"
+    destination: "/nemo/gym/v0.2.1/environment-tutorials/real-world-environment/generating-training-data"
+  - source: "/nemo/gym/v0.2.1/environment-tutorials/real-world-implementation"
+    destination: "/nemo/gym/v0.2.1/environment-tutorials/real-world-environment/resources-server-implementation"
+  - source: "/nemo/gym/latest/environment-tutorials/real-world-data-generation"
+    destination: "/nemo/gym/latest/environment-tutorials/real-world-environment/generating-training-data"
+  - source: "/nemo/gym/latest/environment-tutorials/real-world-implementation"
+    destination: "/nemo/gym/latest/environment-tutorials/real-world-environment/resources-server-implementation"
+  # Version alias: v0.2 → v0.2.1
+  - source: "/nemo/gym/v0.2"
+    destination: "/nemo/gym/v0.2.1"
+  - source: "/nemo/gym/v0.2/:path*"
+    destination: "/nemo/gym/v0.2.1/:path*"
+  # README/blog links that pointed to Sphinx pages whose canonical was renamed in Fern
+  - source: "/nemo/gym/latest/training-tutorials/unsloth-training"
+    destination: "/nemo/gym/latest/training-tutorials/unsloth"
+  - source: "/nemo/gym/latest/apidocs"
+    destination: "/nemo/gym/api/reference/api-reference"
+  - source: "/nemo/gym/latest/environment-tutorials/creating-training-environment"
+    destination: "/nemo/gym/latest/environment-tutorials/single-step-environment"
+  # Version-root index.html: explicit because :path* does not match the empty-path case
+  - source: "/nemo/gym/latest/index.html"
+    destination: "/nemo/gym/latest"
+  - source: "/nemo/gym/v0.2.1/index.html"
+    destination: "/nemo/gym/v0.2.1"
+  - source: "/nemo/gym/main/index.html"
+    destination: "/nemo/gym/main"
+  # Catch-all: Sphinx `.../index.html` → Fern canonical (must precede `.html` catch-all)
+  - source: "/nemo/gym/latest/:path*/index.html"
     destination: "/nemo/gym/latest/:path*"
-  - source: "nemo/gym/v0.2.1/:path*/index.html"
+  - source: "/nemo/gym/v0.2.1/:path*/index.html"
     destination: "/nemo/gym/v0.2.1/:path*"
-  - source: "nemo/gym/:path*/index.html"
+  - source: "/nemo/gym/:path*/index.html"
     destination: "/nemo/gym/:path*"
-  - source: "/latest/about/concepts/training-approaches"
-    destination: "/latest/about/concepts/training"
-  # Legacy page URLs (foo.html); must follow all :path*/index.html rules above
-  - source: "nemo/gym/:path*.html"
+  # Catch-all: Sphinx `foo.html` → Fern canonical `foo`
+  - source: "/nemo/gym/:path*.html"
     destination: "/nemo/gym/:path*"