GET /api/v1/repos/:owner/:name/vision carries an ETag and answers a repeat with 304 until the direction issue changes #9215

GET /api/v1/repos/:owner/:name/vision now carries a weak ETag and answers a repeat with a 304. test/vision-etag.test.ts (5 tests) and the existing test/api-vision.test.ts pass, and tsc --noEmit was clean. I didn't run scripts/gate.ts or the full suite.

• Change: in src/http/api/vision.ts the answer is serialised once and the tag is weakEtag over those exact bytes, so the body is byte-for-byte what it was. Every 200 and 304 carries cache-control: private, no-cache and vary: authorization, cookie. If If-None-Match holds the tag, the route returns a bodiless 304 with the same headers.
• Ordering: the missing-repo 404 and the invalid_number 422 are returned before any tag is computed. They carry no ETag, even with If-None-Match: *.
• What moves the tag: because it's computed over the body, it moves when the direction changes, when a different number is asked for, and when a vision-pull preview appears. The owner and a reader get different tags, so one viewer's tag buys another nothing. A reader and an anonymous visitor are shown the same body, so they do share a tag.
• "Direction issue": in this codebase the direction is repo.autonomy_direction, a column with no title or comments. So the test changes that column and a preview, rather than an issue's body, title and comments.
• Test weakened: the vary assertion uses toContain("authorization, cookie"), because the server appends Accept-Encoding.
• Not done: I didn't touch src/http/api.ts.

To try it, request the route with a token, then repeat it with If-None-Match: <etag>. It should return 304 with no body.

Closes #9202

GET /api/v1/repos/:owner/:name/vision now sends a weak ETag, and a repeat request that holds it gets a 304 with no body.

The check failed because no commit message had a Try: line. I added an empty commit with one, and bun scripts/gate.ts now exits cleanly. I pushed it but haven't seen the forge's re-run, and I didn't re-run the tests, because the code is unchanged since they passed.

What changed

• src/http/api/vision.ts tags the exact bytes it sends with weakEtag.
• Every 200 and 304 carries cache-control: private, no-cache and vary: authorization, cookie.
• The 422 and the missing-repo 404 are returned before any tag is computed, so they carry none, even with If-None-Match: *.
• The tag moves when the direction changes, when a different number is asked for, and when a vision-pull preview appears. The owner and a reader get different tags, so one viewer's tag buys another nothing.
• test/vision-etag.test.ts covers each of these.

Not done

• I left src/http/api.ts alone.
• The issue says "direction issue", but here the direction is the repo.autonomy_direction column, which has no title or comments. The tests change that column and a preview instead.
• The vary assertion uses toContain, because the server appends Accept-Encoding.

Try

• Call GET /api/v1/repos/trevato/forge/vision on the preview with a token.
• Repeat it with If-None-Match set to the etag you got back; the repeat is a 304 with no body.

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