fix(resources): skip post-fetch resolution for direct_proxy reads

[Ewertonslv]

🔗 Related Issue

Closes #5451

📝 Summary

In direct_proxy gateway mode, ResourceService.read_resource fetches the
resource live from the upstream and builds the final TextResourceContents /
BlobResourceContents. Execution then fell through into the shared post-fetch
RESOLVE CONTENT block, whose first branch runs getattr(content, "id")
unconditionally. Those MCP-compliant models (mcpgateway/common/models.py) have
no id field, so every direct_proxy text or blob read raised
AttributeError: 'TextResourceContents' object has no attribute 'id'. The
transport layer catches the exception and returns empty content, so the client
silently receives text="" instead of the fetched payload.

Root cause

The direct_proxy branch never marked its content as already-resolved — the
# Skip the rest of the DB lookup logic comment did not actually skip anything.

Fix

Track whether content came from the direct_proxy branch (direct_proxy_read) and
skip the metadata→content resolution for it. The gateway access check, the
resource access check, and the post-fetch plugin hooks all still run — only the
id-based invoke_resource re-resolution is bypassed, since the payload is final.

Tests (before → after)

The existing happy-path direct_proxy tests masked the bug by monkey-patching
id-bearing subclasses over the real models, so production classes never took the
failing path. This PR adds two regression tests exercising the real
TextResourceContents / BlobResourceContents:

• Without the fix: both raise AttributeError at the getattr(content, "id") call.
• With the fix: text read returns the live text, image/png blob read returns its
  blob, and invoke_resource is asserted not re-awaited.

pytest tests/unit/mcpgateway/services/test_resource_service.py passes locally
(full file green, including module doctests via --doctest-modules).

📏 Reviewability

• This PR has one clear purpose
• The linked issue is not labeled triage
• Unrelated bugs or improvements are tracked in separate issues/PRs
• Tests are included with the code they validate
• If AI-assisted, I understand and can explain the generated changes

🏷️ Type of Change

• Bug fix

[Ewertonslv]

Correction to my checklist above: I ticked "the linked issue is not labeled triage", but #5451 is in fact still labeled triage — I misread the label state when opening this. Apologies. I've commented on the issue with the root-cause analysis so a maintainer can triage it, and I'm happy for this PR to sit until that happens, or to close it if the approach isn't wanted.

For coordination: this and #5467 were opened the same day and both touch read_resource in resource_service.py, but they fix different bugs on different code paths and their hunks don't overlap (lines ~2417 vs ~2430), so they merge cleanly in either order and neither depends on the other. Kept separate deliberately, per the one-concern rule. DCO is signed off.

[jonpspri]

Hi @Ewertonslv — sincere apologies for leaving this PR open for so long without a proper review or merge. That's on us, and we're sorry for the lack of responsiveness.

We're closing this PR now as part of a housekeeping pass on long-open contributions. The linked issue (#5451) remains open, so the need is still tracked.

If you're still interested in contributing this change, please feel free to:

1. Rebase your branch on the current main
2. Re-open this PR (or open a fresh one)

We genuinely appreciate your contribution and hope to give it the attention it deserves. Thank you for taking the time to contribute to ContextForge! 🙏

[Ewertonslv]

Thanks @jonpspri — no problem at all, and thanks for the transparency about the housekeeping pass.

Rebased onto current main (ffcc0822) and re-verified. GitHub would not let me re-open this PR after the rebase (force-pushing the head branch makes a closed PR non-reopenable), so I took the "or open a fresh one" path: #6503.

Same change, only rebased. One conflict, resolved by keeping both sides — main grew the _set_gateway_content helper right above the if isinstance(content, ...) branch, so the helper is untouched and the direct_proxy_read guard now sits in front of it.

The bug is still present on today's main, and the regression tests still prove it: with the production hunk reverted they fail with AttributeError: 'TextResourceContents' object has no attribute 'id'; with it applied they pass, the full test_resource_service.py is green (309 tests), and ruff/black are clean. Details in #6503.