refactor: percent-encode cache key subject instead of hex

[alukach]

What

cache_key_with_subject hand-rolled hex encoding (subj.bytes().map(|b| format!("{:02x}", b))) to make the subject URL-safe in the cache key. The percent_encoding crate — already imported in this file, with a PATH_SEGMENT set already defined — does the same job.

let encoded = utf8_percent_encode(subj, PATH_SEGMENT);

Why

Same guarantee (injective, URL-safe), no hand-rolled encoder, and shorter keys (only non-unreserved bytes get expanded, vs. every byte → 2 hex chars). Reuses tooling the file already pulls in rather than reimplementing it.

Verification

cargo clippy --target wasm32-unknown-unknown clean; full pre-push suite green. utf8_percent_encode returns a Display type so the format! key construction is unchanged.

Found via ponytail over-engineering audit.

🤖 Generated with Claude Code

[claude]

Claude finished @alukach's task in 22s —— View job

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✅ No blocking issues — safe to merge.

• src/cache.rs:121 — utf8_percent_encode with PATH_SEGMENT is a correct drop-in replacement for the hand-rolled hex encoder. Both are injective and URL-safe; the only observable difference is shorter keys for typical ASCII subjects (e.g. a UUID subject passes through unchanged vs. being doubled in length by hex). The Display impl on PercentEncode means format!("{api_url}{sep}subject={encoded}") on line 127 works identically to before.

• The PATH_SEGMENT set (lines 16–20) already encodes % itself (it's in NON_ALPHANUMERIC), so percent-encoded output is round-trip safe — a subject containing a literal % won't be misread as an already-encoded sequence.

• Cache keys generated before this change (hex) and after (percent-encoded) are not compatible, so any cached entries at deploy time will miss and be rehydrated. That's benign given the short TTLs (60–1800 s) and the fact this is a read-through cache.

[github-actions]

🚀 Latest commit deployed to https://source-data-proxy-pr-160.source-coop.workers.dev

• Date: 2026-06-18T23:38:30Z
• Commit: 774aaf5