Zoë: You sanguine about the kinda reception we’re apt to receive on an Alliance ship, Captain?
Mal: Absolutely. What’s “sanguine” mean?
Zoë: Sanguine. Hopeful. Plus, point of interest, it also means “bloody”.
Mal: Well, that pretty much covers all the options, don’t it?
Lukewarm?
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suggestion #1
“hesistant”
Maybe in use with an additional word or two , such as “she accepted it hesitantly”
Suggestion #2
“with reservations”
example: “she agreed, but with reservations”
Nah…the situation described in the OP is more phlegmatic than sanguine.
What a melacholic thought…
That’s the one.
Would ‘Stoicism’ come into this? Again not perfect, but what do you expect? I’m on my lunch break.
It’sallgood. OK, three words, but still… 
According to Keats it’s negative capability:
I found it kinda humourous.
Well, hell, if you want to go that way:
Aporia
…
Aporia (Ancient Greek: ἀπορία: “impasse, difficulty of passing, lack of resources, puzzlement”) denotes in philosophy a philosophical puzzle or state of puzzlement and in rhetoric a rhetorically useful expression of doubt.
…
Definitions of the term aporia have varied throughout history. The Oxford English Dictionary includes two forms of the word: the adjective, “aporetic” which it defines as “to be at a loss,” “impassable,” and “inclined to doubt, or to raise objections”; and the noun form “aporia,” which it defines as the “state of the aporetic” and “a perplexity or difficulty.” The dictionary entry also includes two early textual uses, which both refer to the term’s rhetorical (rather than philosophical) usage.
In George Puttenham’s The Arte of English Poesie (1589) aporia is “the Doubtful, [so] called…because often we will seem to caste perils, and make doubts of things when by a plaine manner of speech we might affirm or deny [them].” In another reference from 1657, J. Smith’s Mystical Rhetoric, the term becomes “a figure whereby the speaker sheweth that he doubteth, either where to begin for the multitude of matters, or what to do or say in some strange or ambiguous thing” (OED). Herbert Weir Smyth’s Greek Grammar (1956) also focuses on the rhetorical usage by defining aporia as “an artifice by which a speaker feigns doubts as to where he shall begin or end or what he shall do or say” (674).
So “aporetic” it is, but with an “I’m OK with it” appended. Sanguine aporia, maybe.
I am thinking resigned or accepting, perhaps passively accepting?
another three worder:
yeah, no, yeah
agnostic.
apprehensive
How about tentative.
The best answer I found on an Australian Yahoo Answers site was “reconciled”.
Well I know a phrase for it, “Good enough for government work.”
Anyway, I think you’ve all missed the best word of all to describe it:
‘resigned’ – having accepted something unpleasant that one cannot do anything about.
I’ve actually used the word “agnostic” for it.
What about nonchalant?
The problem I see with some words like “resigned”, which are cromulent, but denote an air of disappointment, which I don’t think the OP is specifying.