Support new rbuilder releases

[canercidam]

This PR adapts builder-playground to support the new arch and OS based binary naming pattern for rbuilder releases.

[claude]

Claude finished @canercidam's task in 2m 14s —— View job

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Claude PR Review

Review complete. Three issues flagged inline; summary below.

• Read PR diff
• Analyze playground/releases.go changes
• Analyze playground/recipe_yaml.go changes
• Check tests coverage
• Review custom recipe/doc updates
• Post review

Findings

1. playground.yaml:13-14 — commented-out #version: "v1.11.3" left next to active v2.0.0 is dead config without context; either drop it or add a one-line rationale.
2. releases.go:70-79 — the new binary-arch branch duplicates the binary branch almost verbatim; worth collapsing. Also raised a pre-existing partial-download/cache-poisoning issue in downloadBinary that binary-arch inherits (failed mid-transfer leaves a broken file that the next run treats as cached).
3. recipe_yaml.go:654 — the default Arch mapping hardcodes x86_64-unknown-linux-gnu on any Linux host. Pre-existing, but binary-arch encodes arch in the asset path, so linux/arm64 hosts will now fetch the amd64 binary (or 404) instead of aarch64-unknown-linux-gnu, which rbuilder v1.3.15 does publish.

Tests for the new binary-arch path (happy path + unsupported-arch error) look good and use an httptest server consistently with existing tests.
• Branch

[claude]

Claude finished @canercidam's task in 1m 53s —— View job

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Claude PR Review (sync update)

Looking at the new commits since my first pass:

• Diff new commits vs. prior review
• Verify which prior findings were addressed
• Re-check remaining issues still apply

Status of prior findings

1. playground.yaml commented-out version — ✅ addressed by 46125c9. Current line version: "v1.11.3" # v2.0.0 not supported yet gives the rationale inline; no longer dead config.

2. releases.go binary / binary-arch branch duplication + partial-download cache poisoning — ❗ still open. See prior inline comment. The binary-arch branch at releases.go:70-79 still duplicates the binary branch's download-and-chmod logic, and downloadBinary still writes directly to outPath before io.Copy completes — a mid-transfer failure leaves a partial file that the cache check at releases.go:37-43 treats as valid on the next run.

3. recipe_yaml.go Linux arch mapping hardcoded to x86_64 — ❗ still open. See prior inline comment. With binary-arch now encoding arch in the URL, a linux/arm64 host (ARM cloud VMs, Apple Silicon containers) will request rbuilder-v1.3.15-x86_64-unknown-linux-gnu and either 404 or pull an amd64 binary it can't execute. rbuilder v1.3.15 publishes aarch64-unknown-linux-gnu — worth mapping.

The new commits (d1b3858, 46125c9) only touch custom-recipes/rbuilder/bin/playground.yaml and don't introduce new issues.

• Branch •