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Possible patrons including Hierarch Modrons, at the least. Honestly, not sure about many more options. Gods of the forge, inevitables, powerful constructs?

Flying Blade
From 1st level, you gain proficiency with martial weapons.

Additionally, you can use a bonus action to regain your weapons. Any weapon you have dropped, thrown, or had taken from you reappears on your body in the location it was at the end your last turn. This feature cannot repair any weapons, or affect ammunition.

Infused Support
You are infused with the sturdiness of your patron. Your hit points increase by 1 per warlock level, you gain proficiency with medium armor, and you learn the Mold Earth cantrip, which doesn't count against your cantrips known.
These are all over the place, but general buffs for melee combat. Not sure how to reasonably focus them.

Stonewall Strike
From 6th level, when you are hit by an attack, you can give yourself resistance to one damage type dealt by the attack until the end of your next turn. Once you use this ability, you can't use it again until you finish a short or long rest.

Solid Construction
Starting at 10th level, you gain resistance to acid and poison damage. If you regain hit points by spending hit dice at the end of the short rest, you regain an extra 10 hit points.

Create Bodyguard
At 14th level, at he end of a short or long rest you can reach out and touch a section of stone. The stone is converted into a set of armor that you (and only you) can wear. This armor has the stats of a set of animated armor, and uses its own AC and saving throws.

The Armor takes all forms of damage except poison and psychic damage for you, but if your speed is higher than 25 it is reduced to 25 while you wear the armor. Once the armor's HP is reduced to 0, it crumbles and is destroyed.
Bonus hit points, with a reasonable AC.

Spoiler: Invocations
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Builder's Sight
Prerequisite: Empowered Bastion patron

You can see weaknesses in the walls around you, granting you knowledge of where they are weak. You do double damage to structures and have advantage on perception checks to detect secret doors.

Animate Allies
Prerequisite: Empowered Bastion patron, 9th level

You can cast Animate Objects once using a warlock spell slot. You can't do so again until you finish a long rest.

Honestly, a bit shocked I can't seem to find the second invocation in the books. Not sure the first one works alright, given you'd need to roll an extra die when there's a door to find.