Another tactic you could consider is to jump into the hostile system and camp the jump point and deploy your fleets in an ambush configuration. When you are ready, turn on your active sensors and wait for the enemy to close the distance to you. I've done this a few times against similar roboenemies and it's been working rather well.

The blob challenge remains, but it has diminished by the tonnage of one welcoming committee. One more report for now.

Let me just say first as my preliminary observation that there are some interesting fencing manoeuvres to pull off with a non-optimized, inferior fleet against this kind of enemy. The AI has displayed a degree of adaptive behaviour that made this whole enterprise fun.

I plan to probe the question again, if not in this system or this universe, then in another. Looking forward to reading about further ideas and other experiences with these kinds of blobs and their mobile parts, here or elsewhere.

=====

Athena Garden (final)

The operation has been a terrible disaster and a glorious victory.

The build-up (after the backup point): With both our cruisers and more or less half of our beam ships overall in TF Watchman in the inner system, the roboships went through many cycles of wasting/reloading missiles while freighters took detours and delays to move safely to/from the colony.
When the tug with our second weapon platform approached the inner system, the welcoming committee wanted to head for it, but TF Watchman rushed to intercept and they changed course. At one time, the task force briefly came a tad too close and was gently laser-epilated, resulting in two ships being detached and headed for home.
Their fleet retreated, our fleet retreated, and the platform was delivered safely to Pallas, as the colony has been christened by its first mayor. The main Home Fleet with all missile-armed ships and the other beam-half was still far beyond the outer planets near freighters and a supply convoy when: the committee came to greet the colony.

(The HI errors: I'm slowly getting a little better at schizo-managing things; but the point-blank battle began again with a too large increment and the loss of four corvettes. I hope, but can't be absolutely certain that it was truly an AI decision and not increment choice that brought the fleet to the planet.
Subsequently seeing the firepower of the enemy ships in action, those corvettes would probably have gone in the first or second increment anyway. And then more mistakes: I initially forgot to reset the STOs on the planet which had previously been switched to PD. Later I failed to retarget several fire controls for quite a while, a mistake that probably cost a frigate or maybe even two.)

The disaster: In the ensuing battle, we soon lost five corvettes and both our cruisers, then, one by one, all six frigates. The fleet will have to be rebuilt.
Fortunately, the two other cruisers will go to space in two months, and Vaath can spit out four CTs at a time. The frigates will take a while to replace; but Earth's mineral stocks have replenished a little, so there there is room for a reconstruction. Events on the frontier signal that there is also time for it.

The victory: Before exploding, our cruisers landed a few good shots at the three terrible enemy cruisers, the Hydra platforms added their incoherent, but substantial bite, and not long after our two cruisers, their three fireballed. After that, supported by the fully intact weapon platforms and the SDI*, our smaller ships had the upper hand over their larger, but fewer ships.
* [SDI="Static Defence Installation"=ground formation of 6+10 STOs; technologically outdated, but basically sound as far as my now marginally above zero experience with STOs can tell. Much corundium was set aside for SDI construction when isolationists were in power early on. We have even continued to add a few after that; and there will probably be an upgrade one of these years. One is sent to every primary colony of an inhabited system now as a rule; more can be added through federal haggling or as part of frontier defence priorities.]
The only wreckless actors to remain in orbit in the end were ours. The loss is immense, but looking at the destroyed tonnage, adding to the balance a few thousand points in research that will help to close the technological gap, it was a victory.
To honour this great achievement, all survivors have been decorated with a dedicated commemorative pin. Many plan to stick it into soft spots in the surface of armchair admirals back home.

The aftermath: The colony and the two platforms will remain, rotating shifts with a fairly new third at home for overhauls if needed. There are bound to be escorted convoy runs to the colony from time to time to add more population, basic installations and eventually maintenance capacity for the stations. But major Home Fleet operations in Athena are suspended indefinitely.
The remaining enemy forces at Athena IV can wait; they seem to be unable or unwilling to move and the colony is out of observed missile range all year.
(RP bonus: The loss of a substantial part of the fleet makes it highly likely that the two-decade dominance of the current ruling faction will be plausibly broken in the next election. New doctrine and re-designed classes to consider...)

microwaves can help a lot if you reach into beam range thoug, being able to start disabling enemies without needing to go through their armor is very good.

This is the sort of thread that belongs in the Spoiler Races forum, as it discusses the specific capabilites and tactics of (and against) a Spoiler Race.

So I thought. Only, there isn't one in the C# section [yet] unless it's hidden so well that I cannot see it.
I put "spoiler" into the title to make it as obvious as possible.

you can usually bait them away from their stations with your fleet, but if they are losing they sometimes retreat, so you need good speed to close the distance before the stations an support them.

I keep track of the story. I hope it ends well for you. But never ever forget to bring PDs. %17 rof4+ gauss turrets work wonders when they amassed. Only that way you can close the distance. And otherwise I don't think their PD is penetrable with missile salvos unless you spend a fortune on them.

If you get succeed with a different strategy, I'll be happy to hear it.

Odd. In my last game, the Precursors ignored me the first time and long-range missile'd my scout. Second attempt with a small combat fleet had them chase me to the jump point. Barely escaped. Third attempt got ANNIHILATED - some of them stayed and camped the JP. :|

In my experience with Precursors it depends on what weapons they have. I have beam ships waiting at jump point to ambush me, missile ships tend to intercept at missile range and then start to withdraw to location where their orbital defence bases are (most likely to replenish missiles).

Maybe some extremely long range but low damage missiles would do the trick? They would be intended to get the enemy to chase you, not to actually do any useful damage. Then draw them through a trap of your liking.