A great example of a none-too-tricky puzzle that was nevertheless great fun to solve. Nothing particularly arcane (although I did learn one new word); just well-crafted, creative wordplay. Thanks Orense.
ACROSS
1. POSITS I [one, 1] within posts [situations]
4. COUSCOUS Co(mpany) + u(sing) + scous(e) [Liverpudlian: a term taken from Liverpool’s signature dish] to give the North African staple
10. SHAREWARE Anagram of her swear a to give a term for shareable software
11. ARENA Hidden in prepARE NAtional
12. DIET Ie [i.e., id est, that is] within d(entis)t
13. CELEBRATES Anagram of steel brace to give ‘celebrates’ in the sense of ‘observing’ a holiday or festival
15. TRAPEZE Cryptic definition (top signifying the circus ‘Big Top’)
16. THEIST (Dayligh)t + heist [robbery] to give a believer in God
19. RESIDE Re [on, about] + side [edge]: a superbly economical clue
21. PEERAGE Peer [look] + age [mature]
23. ACCREDITED Anagram of cited cadre
25. RIPE Initial letters of R(eckoner) I(s) P(roof) E(nough)
27. ERASE Eras [times] + e(xpress)
28. TERRORISE Error [mistake] within anagram of ties
29. SWEETPEA Wee [small] + t(ime) within spea(k) [talk] to give the climbing flower
30. REPENT RE [Royal Engineers, soldiers] + pent [locked up]
DOWN
1. POSTDATE Post [letters, mail] + date [fruit]
2. STAGE NAME Anagram of mensa get a
3. TREK Reversed within ticKER Tape
5. OVEREAT (C)over [insurance] + eat [worry, in the sense that something might worry or ‘eat at’ you]
6. STARRY-EYED A playful double definition
7. OVERT Over [done] + t(ime)
8. SPARSE Spars [boxes] + e(nergy)
9. RACEME RA [artist, member of the Royal Academy] + CE [church (of England) + me [compiler] to give ‘a type of inflorescence in which the flowers are arranged on short, nearly equal, lateral pedicels, at equal distances along a single elongated axis’, apparently…
14. REFINEMENT RE [Royal Engineers, soldiers (again)] + fine [excellent] + men [people] + t(heir)
17. STABILISE Stab [attempt] + I [1, one] + anagram of lies
18. TENEMENT Men [people (again)] within tenet [dogma]
20. EPISTLE Anagram of piste + le [‘the’ in French] to give something one might read
21. POETRY Poet [Wordsworth, for example] + RY [railway (lines)], with the whole providing the definition
22. WAGERS R(isky) within wages [salary]
24. CRATE C [chemical symbol for Carbon] + rate [charge] to give a slang term for an old banger
26. DOLE (Provide)d + ole [¡Olé!, cheer in Spain] to give what is now officially the Jobseeker’s Allowance
A nice pleasant stroll of a solve, though there were one or two clever misdirections – such as in 4a where it was necessary to separate ‘Liverpudlian’ from ‘dish’; the latter being the single word definition.