Thank you to Zamorca. Definitions are underlined in the clues.
Across
1. Posts soldiers to guard heavy artillery, initially two in position (3-5)
JOB-SHARE : JOBS(posts/positions in an organisation) + RE(abbrev. for the Royal Engineers in the British army) containing(to guard) 1st letters, respectively, of(…, initially) “heavy artillery“.
Defn: Two people each working part-time doing the same job.
6. Discover the truth about doctor during convention (6)
RUMBLE : MB(abbrev. for “Medicinae Baccalaureus”/Bachelor of Medicine/a doctor) contained in(during) RULE(convention/the normal or customary state of things, as in “… the exception rather than the rule”).
9. Fund cultivation of vines east of Meursault (6)
INVEST : Anagram of(cultivation of) [VINES + last letter of(east of, in an across clue) “Meursault“].
10. Someone emptied out case to find drug (8)
SEDATIVE : “Someone” minus all its inner letters(emptied) + DATIVE(in grammar, one of the cases/forms of a noun, adjective or pronoun).
11. Dam river that is wide going west (4)
WEIR : Reversal of(… going west, in an across clue) [ R(abbrev. for “river”) + IE(abbrev. for “id est”/that is) + W(abbrev. for “wide”) ].

12. Schedule this month’s one that can’t be changed (3,2,5)
SET IN STONE : SET(to schedule/to make arrangements for something to be done, as in “to set someone to do a task”) + INST(abbrev. for “instant” indicating this/present month, as in “your letter of the 16th inst.”) + ONE.
14. Pretty fine engraving (8)
FETCHING : F(abbrev. for “fine”) + ETCHING(an engraving/a print produced by carving on a surface).
A fetching etching:

16. Wipe out daughter in card game (4)
UNDO : D(abbrev. for “daughter”) contained in(in) UNO(a card game using a specially printed deck).
Defn: …/cancel the effects of a previous action).
18. Piece of land returned in slander case (4)
ACRE : Reversal of(returned …) hidden in(in) “slander case“.
19. Free seats bound to be grabbed in cafés (3,5)
TEA SHOPS : Anagram of(Free) SEATS containing(… to be grabbed) HOP(to bound/to jump a short distance).
21. Rushes broken by May storms (10)
HURRICANES : HURRIES(rushes/moves with haste) containing(broken by) CAN(may, indicating the possibility of something being done)
22. Emperor‘s last letter penned in vehicle (4)
CZAR : Z(last letter in the English alphabet) contained in(penned in) CAR(a motor vehicle).
24. Manor in France where setter’s come back for cheese (8)
HALLOUMI : HALL(a manor/a large country house with land) + OÙ(French for “where”) + reversal of(… come back) I’M(setter’s, with the setter using the self-referential pronoun).
… that doesn’t melt:

26. Raucous-sounding call over wood (6)
CROAKY : CRY(call/shout) containing(over) OAK(wood from the, well, oak tree).
27. Routine enthrals old time musicians (6)
SEXTET : SET(routine/fixed as the procedure to be followed) containing(enthrals) [ EX-(prefix indicating “former”/old) + T(abbrev. for “time”) ].
28. Wash blue tights first (4,4)
HOSE DOWN : DOWN(blue/feeling sad) placed after(… first) HOSE(tights/close fitting garments for women covering legs, hips and bottom.
Down
2. Unesco scheme has not succeeded for snow leopard (5)
OUNCE : Anagram of(… scheme) “Unesco” minus(has not) “s”(abbrev. for “succeeded”).

3. Stays away from direct sunlight (6,5)
STEERS CLEAR : STEER(to direct/to control the movement of) + S(abbrev. for “sun”) + CLEAR(light/free of cloud, and with much natural light).
4. First of teak inlaid carvings on new sitar is beautifully designed (8)
ARTISTIC : 1st letters, respectively, of(First of) “teak inlaid carvings” placed below(on, in a down clue) anagram of(new) SITAR.
5. Friendly way the egotist affected keeps working (4,2,3,2,4)
EASY TO GET ON WITH : Anagram of(… affected) WAY THE EGOTIST containing(keeps) ON(working, as with an electrical appliance).
6. Go off carrying little house for one’s guinea pig (6)
RODENT : ROT(to go off/to decay and become inedible) containing(carrying) DEN(a little house/a hideout for one).
7. Friend’s lost key found by door (3)
MAT : “mate”(informal term for “friend”) minus(…’s lost) “e”(in music, the keynote/first note of the E major key/scale).

8. Quick pole dance finally gets party animated (7,2)
LIVENED UP : LIVE(quick/animated) + N(abbrev. for “north”, one of the geographic poles) + last letter of(… finally) “dance” plus(gets) DUP(abbrev. for the Democratic Unionist Party of Northern Ireland).
13. Evoke sympathy when husband in coach tour accident died (5,1,5)
TOUCH A CHORD : H(abbrev. for “husband”) contained in(in) anagram of(… accident) COACH TOUR + D(abbrev. for “died”).
15. Rant after Edward’s new company uniform gets egg on (9)
ENCOURAGE : RANT(to rage/to express anger) placed under(after, in a down clue) [ E(abbrev. for “Edward”, as in “ER”?) + N(abbrev. for “new”) + CO(abbrev. for “company”, a commercial concern, say) + U(abbrev. for “uniform”) ].
17. Managed taking bags with rifles through (8)
RANSACKS : RAN(managed, an organisation, say) plus(taking) SACKS(large bags made of strong material).
20. Resign following a top criminal’s reprieve (6)
ACQUIT : QUIT(to resign/to relinquish a position) placed below(following, in a down clue) [A + 1st letter of(top, in a down clue) “criminal” ].
23. No sense in punishing weaknesses – it’s out of line (5)
ASKEW : “sense” deleted from(No … in) anagram of(punishing) “weaknesses”.
25. Briefly informed about situation (3)
LOT : Reversal of(… about) “told”(informed/given knowledge of) minus its last letter(Briefly …).
Defn: …/in life, the circumstances one finds oneself in.
Liked this pangram, although I felt 6d should have ended with a question mark and E for Edward in ER is ok but by itself – well I’m not convinced. My favourite was ASKEW.
Clearly you meant to write EX for old 27a.
Thanks Hovis. Blog amended.
A hard-earned pangram from Zamorca which teased the old brain and helped to reel in 1a.
I liked OUNCE, SEDATIVE and RUMBLE best in an enjoyable grid overall. Guessed but couldn’t parse 16a.
Thanks to Zamorca and Scchua.
Good to see the pangram at the end, with some not so easy parsing, eg for LIVENED UP and ENCOURAGE along the way. JOB SHARE was one of my last in as well.
It still doesn’t look quite right, but I had ‘for one’s guinea pig’ as the def for RODENT, which would obviate the need for the question mark as suggested by Hovis @1.
Thanks to Zamorca and scchua
I see what you mean, WordPlodder. I admit that I took “for one’s” as filler, which is unfair on my part.
Excellent pangram, although that didn’t help me get 1a as it should have. “Discover the truth” as a meaning for “rumble” was new to me; glad to learn that. And “croaky” was a new word to me , but clearly the answer given the surface and the cross letters. I needed the blog to explain DUP in 8d. Otherwise, it felt straightforward. The long anagram in 5d was my favorite.
In 6d, could “for one’s” be interpreted as “an example is”?
Thanks Zamorca and Scchua.
EdK @6 That’s how I read WordPlodder’s comment. An unusual wording which passed me by when solving.
Hovis@7: I didn’t interpret his comment that way at first, but now that you pointed it out, I agree completely.
Thanks Zamorca and scchua
Another toughish puzzle early in the week that took over the hour to get complete and found the left hand side harder than the right. Got off to a quick enough start with the crossword favourite cat at 2d, but the rest of the journey was just steady but enjoyable work. Was sort of aware of a pangram potential, but didn’t really home in on it and it certainly didn’t help in the end.
Finished in the SW corner with LOT, SEXTET and ACQUIT (where the last two would’ve been helped a lot with the pangram knowledge).