Clarify which budget limit blocked a conversation

[ZeroPoint95]

Changelog

• Help unblock conversations after budget overruns: errors now name /budget conversation or /budget day. Previously, the generic hint could change the daily allowance while leaving the conversation blocked.
• Clarify that the daily budget covers all conversations; add a separate /budget conversation tip. Each tip retires independently.
• Explain that both limits apply, with examples and recovery steps. Test recovery in the same running conversation; budget enforcement is unchanged.

Related Notion issue

Validation: CI green; focused hint tests and local pr-ready gates for both follow-ups passed. The original full local gate had four session failures reproduced on clean dev.

[AbirAbbas]

Taking over: I pushed two manual commits. Nothing blocks this PR.

I checked this by hand in the real binary against a dev build, with tiny limits: conversation limit hit, daily limit hit, both hit, and neither set. I ran every case on both the engine road and codeaf chat --no-host.

• On dev, the refusal said /budget changes it. /budget 20 answered per day · $20, and the next send was refused again. That is the confusion you described.
• On this branch, the refusals name /budget conversation or /budget day, and each one releases the same running conversation. Both roads show the same words, and the tips retire separately.

Pushed:

• 03d5087aa manual: "my budget command doesn't work" and "why is my conversation blocked" reached no budget page. The section heading now uses those words, and chat_test.go has four new probes for them.
• 02ca2065e manual: the Spending doors table and starting-codeaf.md still named bare /budget as the conversation limit. The daily limit counts tasks too, not only conversations. The pages also said a refused message stays in the box. It doesn't, on dev either, so they now say ↑ brings it back. The change entry records that correction.

Left for you, none blocking:

• Should a limit refusal put the text back in the box? The comment in rail.go and the old manual both assumed it did.
• With both limits reached, only the daily one is named, so the second only shows up on the next send. One line naming both would save a step.
• The daily tip in notice.go says "across all conversations", but tasks count too.
• The refusal is drawn as error: conversation limit reached …, while the manual quotes it without error:. That predates this PR.
• Over --host, /budget day writes this machine's profile while the remote engine checks its own. I found this reading the code and didn't reproduce it; it predates this PR.
• A project's own conversation limit still wins over the /budget conversation default for new conversations there.
• compaction: summaries as the last step, recovery that fits, and a record that stays #1658 also appends a section at the end of models-and-cost.md, so one of the two will need a keep-both merge.

make pr-ready was green apart from internal/session task-timing tests at load 12–28. Different tests failed on each run, and all of them pass when re-run alone. The push is Markdown plus four manual probes.

[AbirAbbas]

Merged dev in (9e5564c28) after #1658 landed. Both PRs appended a section at the end of models-and-cost.md, so the merge keeps both, the budget section first. go test ./internal/manual/ and the four budget tests pass on the merged tree.

[AbirAbbas]

Reviewed and hand-verified; see the comments above.