fix(pixel-chat): reject empty attempt string in chat result store key

[Vishaaallll]

Why this matters

In ods/extensions/services/dashboard-api/pixel_chat_results.py, ChatResultStore.reserve(self, key, fingerprint) unpacks key directly into SQL queries without verifying that all 3 components (owner, chat, attempt) are non-empty strings. If empty strings or incorrect tuple lengths are passed, malformed records are inserted into the SQLite database, causing primary key collisions or orphaned SSE receipt attempts.

This surgical fix validates that key is a 3-element tuple or list of non-empty strings, raising ValueError("Invalid result store key") otherwise.

Validation

• Baseline reproduction: verified that store.reserve(("", "chat1", "att1"), "fp") inserted rows with empty strings on baseline.
• Post-fix behavior: properly rejects empty or improperly sized key tuples with ValueError.
• Telemetry: pixel-chat suite: 2 passed. New-test syntax and diff checks pass; new regression wired into Linux CI.

Overlap check

Inspected open/closed PRs. PR #5695 touched chat cancellation; zero overlap with store key validation in pixel_chat_results.py.

Risk / AI disclosure

AI-assisted investigation, patch, and regression tests. Strictly defends store key integrity before database transactions. Independent review remains a gate.

Follow-up integration evidence

Composed locally with public-beta at 4fa6ad170 without conflicts. CI and unit checks pass.

[Lightheartdevs]

Thanks for this contribution. public-beta was promoted into main on 2026-09-24 and no longer receives changes, so we're closing pull requests that target it. This isn't a judgment on the change itself. If it's still needed, please rebase onto main and open a focused PR. See #7253 for details and the contribution policy.