fix: treat Go pseudo-versions as unknown server versions

[dal00]

Problem

Headscale's untagged builds — the per-commit main-* and development Docker images — report a Go pseudo-version from GET /version, e.g.:

v0.0.0-20260703052708-048308511c72

parseServerVersion matches this against the semver regex successfully, so it comes back as 0.0.0 with unknown: false. Every capability in capabilitiesFor() is then denied, and the UI shows "Agent requires Headscale 0.28 or newer" against a server that is actually running the newest code on main.

The existing design intent (per the comment on ServerVersion.unknown) is that unrecognizable versions like dev should be treated as fully capable so modern code paths get exercised. A Go pseudo-version is exactly such a dev build — it just happens to parse.

Fix

Detect the pseudo-version shape — 0.0.0 with a <14-digit timestamp>-<12-hex sha> prerelease — and return unknown: true for it, same as dev. A genuine 0.0.0 prerelease (e.g. v0.0.0-beta.1) still parses normally.

Testing

• Added a unit test for the pseudo-version case and a guard test that v0.0.0-beta.1 is not flagged unknown
• pnpm vitest run --project unit tests/unit/headscale/server-version.test.ts — 14/14 pass
• Hit this in production running headscale/headscale:main-0483085 behind Headplane 0.7.0; with this change the agent gate passes

🤖 Generated with Claude Code

[pullfrog]

✅ No new issues found.

Reviewed changes — Detects Go module pseudo-versions from untagged Headscale builds and treats them as unknown server versions so capability gating doesn't lock out main-* / development images.

• Adds a GO_PSEUDO_VERSION_PRERELEASE_RE regex in app/server/headscale/api/server-version.ts to identify the <14-digit-timestamp>-<12-hex-sha> prerelease shape.
• Marks v0.0.0-YYYYMMDDhhmmss-abcdefabcdef as unknown: true, matching the existing dev handling so modern code paths are exercised.
• Adds unit tests covering the pseudo-version case and a guard ensuring a genuine v0.0.0-beta.1 prerelease is not flagged unknown.

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