docs(cache): Clarify custom cache key behavior with single-file purge

[mbullock1986]

Cache Rules that set custom cache keys require API purge with headers/cookies rather than dashboard single-file purge. This clarification reduces customer escalations about why single-file purge does not invalidate cached resources.

Also updates the purge compatibility note in Cache Rules settings to reference the detailed limitations page.

Changes

• cache/how-to/cache-rules/index.mdx: Added Cache Rules and cache keys section
• cache/how-to/purge-cache/purge-by-single-file.mdx: Added Limitations and alternatives
• cache/how-to/cache-rules/settings.mdx: Updated purge compatibility note
• changelog/rules/2026-07-16-cache-rules-bot-fields-asn.mdx: Changelog entry for bot fields

[cloudflare-docs-bot]

Review

💡 1 suggestion found in commit da8cce7.

Fix in your agent

Fix the following review findings in PR #32135 (https://github.com/cloudflare/cloudflare-docs/pull/32135).

Before making changes, review each finding and present a brief summary table:
- For each finding, state whether you agree, disagree, or need clarification
- If you disagree (e.g. the fix requires disproportionate effort for minimal benefit,
  or the finding is factually incorrect), explain why
- If you need clarification before deciding, ask those questions
- Then share your plan for which issues to tackle and in what order

After triaging, fix all legitimate findings. For any you decide to skip,
post a comment on this PR with the finding ID and your reasoning.

---

## Style Guide Review

### Suggestions (1)

#### SG-b7daeb8099bd · Oxford comma
- **File:** `src/content/docs/cache/how-to/purge-cache/purge-by-single-file.mdx` line 36
- **Issue:** List of three or more items lacks a comma before the conjunction: "headers, cookies, or other request properties"
- **Fix:** Add a serial comma: "headers, cookies, or other request properties" → "headers, cookies, or other request properties"

Code Review

This code review is in beta and may not always be helpful — use your judgment.

_{No code review issues found.}

Conventions

_{No convention issues found.}

Style Guide Review

Suggestions (1)

File	Issue
cache/how-to/purge-cache/purge-by-single-file.mdx line 36	Oxford comma — List of three or more items lacks a comma before the conjunction: "headers, cookies, or other request properties" Fix: Add a serial comma: "headers, cookies, or other request properties" → "headers, cookies, or other request properties"

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[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/content/changelog/	@cloudflare/pm-changelogs, @cloudflare/product-owners
/src/content/docs/cache/	@cloudflare/product-owners, @ack-cf, @zaidoon1

[github-actions]

Nimbus Preview URL: https://nimbus-da8cce74.preview.developers.cloudflare.com
Nimbus Preview Branch URL: https://nimbus-cache-rules-custom-key-purge-docs.preview.developers.cloudflare.com

[github-actions]

Preview URL: https://da8cce74.preview.developers.cloudflare.com
Preview Branch URL: https://cache-rules-custom-key-purge-docs.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/cache/how-to/purge-cache/purge-by-single-file/	https://cache-rules-custom-key-purge-docs.preview.developers.cloudflare.com/cache/how-to/purge-cache/purge-by-single-file/
https://developers.cloudflare.com/changelog/post/2026-07-16-cache-rules-bot-fields-asn/	https://cache-rules-custom-key-purge-docs.preview.developers.cloudflare.com/changelog/post/2026-07-16-cache-rules-bot-fields-asn/
https://developers.cloudflare.com/cache/how-to/cache-rules/	https://cache-rules-custom-key-purge-docs.preview.developers.cloudflare.com/cache/how-to/cache-rules/
https://developers.cloudflare.com/cache/how-to/cache-rules/settings/	https://cache-rules-custom-key-purge-docs.preview.developers.cloudflare.com/cache/how-to/cache-rules/settings/

[mbullock1986]

Skipped: SG-23d12b43f00e — The passive voice finding on line 25 of purge-by-single-file.mdx refers to existing text that was already present before this PR (the 'How to purge a single file' section). Since this is pre-existing content and not part of the changes introduced here, I'm skipping it to avoid scope creep. Happy to address it in a follow-up if needed.

[mbullock1986]

Skipped: CR-27c2fe46e171 — Already fixed in the previous round of review. The current file shows (no leading dot).

Skipped: SG-34e3db81e722 — Already fixed in the previous round. The 'What to do instead' section under 'Cache Rules that match on request properties' was rewritten as prose paragraphs (lines 51-53), not a bullet list.

Skipped: SG-69291c84f3d9 — Already fixed in the previous round. The note in settings.mdx was rewritten as a single prose sentence (line 40), not a bullet list.

[mbullock1986]

Skipped: CR-27c2fe46e171 — Already fixed in the previous round of review. The current file shows cf.bot_management.bot_tags["<TAG>"] (no leading dot).

Skipped: SG-34e3db81e722 — Already fixed in the previous round. The "What to do instead" section under "Cache Rules that match on request properties" was rewritten as prose paragraphs (lines 51-53), not a bullet list.

Skipped: SG-69291c84f3d9 — Already fixed in the previous round. The note in settings.mdx was rewritten as a single prose sentence (line 40), not a bullet list.